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J.B. Rosenzweig

First Name: James

Middle Name: B

Last Name: Rosenzweig

Full Name: J.B. Rosenzweig

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444 papers
title: Measurements of Copper RF Surface Resistance at Cryogenic Temperatures for Applications to X-Band and S-Band Accelerators
format: conference proceeding
conference: IPAC 2016
year: 2016
11 authors: A. Cahill | A. Fukasawa | J.B. Rosenzweig | Y. Higashi | G.B. Bowden | V.A. Dolgashev | J. Guo | M. Franzi | S. Tantawi | P.B. Welander | C. Yoneda
abstract: Recent SLAC experiments with cryogenically cooled X- band standing wave copper accelerating cavities have shown that these structures can operate with accelerating gradi- ents of 250 MV/m and low breakdown rates. These results prompted us to perform systematic studies of copper rf prop- erties at cryogenic temperatures at low rf power. We placed copper cavities into a cryostat with a cryocooler, so the cavities could be reduced to 4K. We used different shapes of cavities for the X-band and S-band measurements. RF properties of the cavities were measured using a network analyzer. We calculated rf surface resistance from measured Q 0 at temperatures from 4 K to room temperature. The re- sults were then compared to the theory proposed by Reuter and Sondheimer. These measurements are part of studies with the goal of reaching very high operating accelerating gradients in normal conducting rf structures.
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title: Observation of redshifting and harmonic radiation in inverse Compton scattering
format: journal article
publisher:
year: 2015
21 authors: Y. Sakai | I. Pogorelsky | O. Williams | F.H. O'Shea | S. Barber | I. Gadjev | J. Duris | P. Musumeci | M. Fedurin | A. Korostyshevsky | B. Malone | C. Swinson | G. Stenby | K. Kusche | M. Babzien | M. Montemagno | P. Jacob | Z. Zhong | M. Polyanskiy | V. Yakimenko | J.B. Rosenzweig
abstract: Inverse Compton scattering of laser photons by ultrarelativistic electron beam provides polarized x- to γ-ray pulses due to the Doppler blueshifting. Nonlinear electrodynamics in the relativistically intense linearly polarized laser field changes the radiation kinetics established during the Compton interaction. These are due to the induced figure-8 motion, which introduces an overall redshift in the radiation spectrum, with the concomitant emission of higher order harmonics. To experimentally analyze the strong field physics associated with the nonlinear electron-laser interaction, clear modifications to the angular and wavelength distributions of x rays are observed. The relativistic photon wave field is provided by the ps CO2 laser of peak normalized vector potential of 0.5
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title: Single-Shot Coherent Diffraction Imaging of Microbunched Relativistic Electron Beams for Free-Electron Laser Applications
format: journal article
publisher: Physical Review Letters
year: March 2013
10 authors: A. Marinelli | M. Dunning | S. Weathersby | E. Hemsing | D. Xiang | G. Andonian | F.H. O'Shea | Jianwei Miao | C. Hast | J. B. Rosenzweig
abstract: With the advent of coherent x rays provided by the x-ray free-electron laser (FEL), strong interest has been kindled in sophisticated diffraction imaging techniques. In this Letter, we exploit such techniques for the diagnosis of the density distribution of the intense electron beams typically utilized in an x-ray FEL itself. We have implemented this method by analyzing the far-field coherent transition radiation emitted by an inverse-FEL microbunched electron beam. This analysis utilizes an oversampling phase retrieval method on the transition radiation angular spectrum to reconstruct the transverse spatial distribution of the electron beam. This application of diffraction imaging represents a significant advance in electron beam physics, having critical applications to the diagnosis of high-brightness beams, as well as the collective microbunching instabilities afflicting these systems.
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title: Observation of emission process in hydrogen-like nitrogen Z-pinch discharge with time integrated soft X-ray spectrum pinhole image
format: journal article
publisher: Physics of Plasmas
year: February 2013
15 authors: Y. Sakai | J. Rosenzweig | H. Kumai | Y. Nakanishi | Y. Ishizuka | S. Takahashi | T. Komatsu | Y. Xiao | H. Bin | Z. Quishi | Y. Hayashi | I. Song | T. Kawamura | M. Watanabe | E. Hotta
abstract: The emission spectra of hydrogen-like nitrogen Balmer at the wavelength of 13.4 nm in capillary Z-pinch discharge plasma are experimentally examined. Ionization to fully strip nitrogen at the pinch maximum, and subsequent rapid expansion cooling are required to establish the population inversion between the principal quantum number of n¼2 and n¼3. The ionization and recombination processes with estimated plasma parameters are evaluated by utilizing a time integrated spectrum pinhole image containing radial spatial information. A cylindrical capillary plasma is pinched by a triangular pulsed current with peak amplitude of 50 kA and pulse width of 50 ns.
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title: Using the Relativistic Two-Stream Instability for the Generation of Soft-X-Ray Attosecond Radiation Pulses
format: journal article
publisher: Physical Review Letters
year: February 2013
3 authors: A. Marinelli | E. Hemsing | J. B. Rosenzweig
abstract: In this Letter we discuss a novel method for generating ultrashort radiation pulses using a broadband two-stream instability in an intense relativistic electron beam. This method relies on an electron beam having two distinct two-energy bands. The use of this new high brightness electron beam scenario, in combination with ultrashort soft x-ray pulses from high harmonic generation in gas, allows the production of high power attosecond pulses for ultrafast pump and probe experiments.
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title: Generation of Coherent Broadband Photon Pulses with a Cascaded Longitudinal Space-Charge Amplifier
format: journal article
publisher: Physical Review Letters
year: 2013
9 authors: A. Marinelli | E. Hemsing | M. Dunning | D. Xiang | S. Weathersby | F. O'Shea | I. Gadjev | C. Hast | J.B. Rosenzweig
abstract: The longitudinal space-charge amplifier has been recently proposed by Schneidmiller and Yurkov as an alternative to the free-electron laser instability for the generation of intense broadband radiation pulses [Phys. Rev. ST Accel. Beams 13, 110701 (2010)]. In this Letter, we report on the experimental demonstration of a cascaded longitudinal space-charge amplifier at optical wavelengths. Although seeded by electron beam shot noise, the strong compression of the electron beam along the three amplification stages leads to emission of coherent undulator radiation pulses exhibiting a single spectral spike and a single transverse mode. The on-axis gain is estimated to exceed 4 orders of magnitude with respect to spontaneous emission.
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title: Coherent optical vortices from relativistic electron beams
format: journal article
publisher: Nature Physics
year: 2013
7 authors: E. Hemsing | A. Knyazik | M. Dunning | D. Xiang | A. Marinelli | C. Hast | J.B. Rosenzweig
abstract: Recent advances in the production and control of high-brightness electron beams (e-beams) have enabled a new class of intense light sources based on the free electron laser (FEL) that can examine matter at ångstrom length and femtosecond time scales. The free, or unbound, electrons act as the lasing medium, which provides unique opportunities to exquisitely control the spatial and temporal structure of the emitted light through precision manipulation of the electron distribution. We present an experimental demonstration of light with orbital angular momentum (OAM; ref.) generated from a relativistic e-beam rearranged into an optical scale helix by a laser. With this technique, we show that a Gaussian laser mode can be effectively up-converted to an OAM mode in an FEL using only the e-beam as a mode-converter. Results confirm theoretical predictions and pave the way for the production of coherent OAM light with unprecedented brightness down to hard X-ray wavelengths for wide ranging applications in modern light sources.
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title: Stable Charged-Particle Acceleration and Focusing in a Laser Accelerator Using Spatial Harmonics
format: journal article
publisher: Physical Review Letters
year: October 2012
4 authors: B. Naranjo | A. Valloni | S. Putterman | J. B. Rosenzweig
abstract: Regarding the laser-driven acceleration of charged particles in photonic systems, a central unmet challenge is the achievement of simultaneous transverse and longitudinal stability at nonultrarelativistic energies. At such energies, Earnshaw’s theorem [S. Earnshaw, Trans. Cambridge Philos. Soc. 7, 97 (1842)] indicates that a synchronous accelerating wave gives a defocusing effect. We present a scheme in which particles are accelerated by interaction with a resonant spatial harmonic and are focused by strong ponderomotive interaction with nonresonant spatial harmonics. We show that this scheme exhibits net transverse focusing and longitudinal stability, and we discuss its use in a compact laser accelerator.
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title: Time-domain measurement of a self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering
format: journal article
publisher: Applied Physics Letters
year: 24 Sep 2012
2 authors: Gabriel Marcus | J.B. Rosenzweig
abstract: We report, with an unequivocal time-domain measurement, that an appropriately chosen undulator taper can compensate for an electron beam longitudinal energy-chirp in a free-electron laser amplifier, leading to the generation of single-spike radiation close to the Fourier limit. The measurements were taken using the frequency-resolved optical gating technique by employing an advanced transient-grating diagnostic geometry. The reconstructed longitudinal radiation characteristics are compared in detail to prediction from time-dependent three-dimensional simulations.
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title: Beyond Injection: Trojan Horse Underdense Photocathode Plasma Wakefield Acceleration
format: conference proceeding
conference: AAC 2012 15th
year: 2012
18 authors: B. Hidding | J.B. Rosenzweig | Y.Xi | B. O'Shea | G. Andonian | D. Schiller | S. Barber | O. Williams | G. Pretzler | T. Königstein | F. Kleeschulte | M.J. Hogan | M. Litos | S. Corde | W.W. White | P. Muggli | D.L. Bruhwiler | K. Lotov
abstract: An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed ”Trojan Horse” acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam- driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment ”E-210: Trojan Horse Plasma Wakefield Acceleration” has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.
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title: Three dimensional analysis of longitudinal plasma oscillations in a thermal relativistic electron beam: Application to an initial value problem
format: journal article
publisher: Physics of Plasmas
year: 2012
3 authors: A. Marinelli | E. Hemsing | J.B. Rosenzweig
abstract: In this paper, we study the initial value problem of longitudinal plasma oscillations in a relativistic electron beam. Our analysis is based on the formalism developed in Marinelli et al. [Phys. Plasmas 18, 103105 (2011)]. We study the evolution of an arbitrary six-dimensional phase-space perturbation under the effect of longitudinal space-charge forces, with the inclusion of three-dimensional effects due to the finite size of the beam, transverse betatron motion, and longitudinal thermal motion induced by both energy-spread and transverse emittance. We expand the phase-space perturbation in a series of eigenmodes of a Schrödinger-like equation, corresponding to a set of propagating space-charge waves. We develop a general formalism, which we use to find explicit expressions for the evolution of an initial perturbation coupled to the fundamental plasma eigenmode. This work has important applications in the theory of space-charge instabilities in high brightness electron beams and control of shot-noise in seeded free-electron lasers. We discuss the application of the present theory to a specific experimental scenario corresponding to a shot-noise suppression scheme at optical wavelengths.
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title: Experimental observation of helical microbunching of a relativistic electron beam
format: journal article
publisher: Applied Physics Letters
year: 2012
8 authors: E. Hemsing | A. Knyazik | F. O'Shea | A. Marinelli | P. Musumeci | O. Williams | S. Tochitsky | J.B. Rosenzweig
abstract: Experimental observation of the microbunching of a relativistic electron beam at the second harmonic interaction frequency of a helical undulator is presented. The microbunching signal is observed from the coherent transition radiation of the electron beam and indicates experimental evidence of a dominantly helical electron beam density distribution. This result is in agreement with theoretical and numerical predictions and provides a proof-of-principle demonstration of proposed schemes designed to generate light with orbital angular momentum in high-gain free-electron lasers.
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title: Self-Amplified Spontaneous Emission Free-Electron Laser with an Energy-Chirped Electron Beam and Undulator Tapering
format: journal article
publisher: Physical Review Letters
year: 8 April 2011
41 authors: L. Giannessi | A. Bacci | M. Bellaveglia | F. Briquez | M. Castellano | E. Chiadroni | A. Cianchi | F. Ciocci | M.E. Couprie | L. Cultrera | G. Dattoli | D. Filippetto | M. Del Franco | G. Di Pirro | M. Ferrario | L. Ficcadenti | F. Frassetto | A. Gallo | G. Gatti | M. Labat | Gabriel Marcus | M. Moreno | A. Mostacci | E. Pace | A. Petralia | V. Petrillo | L. Poletto | M. Quattromini | J.V. Rau | C. Ronsivalle | J.B. Rosenzweig | A.R. Rossi | V. Rossi Albertini | E. Sabia | M. Serluca | S. Spampinati | I. Spassovsky | B. Spataro | V. Surrenti | C. Vaccarezza | C. Vicario
abstract: We report the first experimental implementation of a method based on simultaneous use of an energy chirp in the electron beam and a tapered undulator, for the generation of ultrashort pulses in a self-amplified spontaneous emission mode free-electron laser (SASE FEL). The experiment, performed at the SPARC FEL test facility, demonstrates the possibility of compensating the nominally detrimental effect of the chirp by a proper taper of the undulator gaps. An increase of more than 1 order of magnitude in the pulse energy is observed in comparison to the untapered case, accompanied by FEL spectra where the typical SASE spiking is suppressed.
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title: Longitudinal profile diagnostic scheme with subfemtosecond resolution for high-brightness electron beams
format: journal article
publisher: PRSTAB
year: 7/13/2011
7 authors: G. Andonian | E. Hemsing | D. Xiang | P. Musumeci | A. Murokh | S. Tochitsky | J.B. Rosenzweig
abstract: High-resolution measurement of the longitudinal profile of a relativistic electron beam is of utmost importance for linac based free-electron lasers and other advanced accelerator facilities that employ ultrashort bunches. In this paper, we investigate a novel scheme to measure ultrashort bunches (subpico- second) with exceptional temporal resolution (hundreds of attoseconds) and dynamic range. The scheme employs two orthogonally oriented deflecting sections. The first imparts a short-wavelength (fast temporal resolution) horizontal angular modulation on the beam, while the second imparts a long-wavelength (slow) angular kick in the vertical dimension. Both modulations are observable on a standard downstream screen in the form of a streaked sinusoidal beam structure. We demonstrate, using scaled variables in a quasi-1D approximation, an expression for the temporal resolution of the scheme and apply it to a proof- of-concept experiment at the UCLA Neptune high-brightness injector facility. The scheme is also investigated for application at the SLAC NLCTA facility, where we show that the subfemtosecond resolution is sufficient to resolve the temporal structure of the beam used in the echo-enabled free-electron laser. We employ beam simulations to verify the effect for typical Neptune and NLCTA parameter sets and demonstrate the feasibility of the concept.
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title: Resonant excitation of coherent Cerenkov radiation in dielectric lined waveguides
format: journal article
publisher:
year: 2011
12 authors: G. Andonian | O. Williams | X. Wei | P. Niknejadi | E. Hemsing | J. B. Rosenzweig | P. Muggli | M. Babzien | M. Fedurin | K. Kusche | R. Malone | V. Yakimenko
abstract: We report the observation of coherent Cerenkov radiation in the terahertz regime emitted by a relativistic electron pulse train passing through a dielectric lined cylindrical waveguide. We describe the beam manipulations and measurements involved in repetitive pulse train creation including comb collimation and nonlinear optics corrections. With this technique, modes beyond the fundamental are selectively excited by use of the appropriate frequency train. The spectral characterization of the structure shows preferential excitation of the fundamental and of a higher longitudinal mode.
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title: Harmonic radiation of a relativistic nonlinear inverse Compton scattering using two laser wavelengths
format: journal article
publisher:
year: 2011
9 authors: Y. Sakai | O. Williams | G. Andonian | A. Fukasawa | E. Hemsing | A. Marinelli | S. Barber | F.H. O'Shea | J.B. Rosenzweig
abstract: The use of two different wavelength lasers in the nonlinear regime of the inverse Compton scattering interaction is proposed in order to provide a new strategy for controlling scattered photon energy distributions in the x-ray to γ-ray spectral region. In this nonlinear interaction, the component of the relativistic electron’s trajectory driven by a longer-wavelength laser with the normalized vector potential aL∼1 is a large oscillatory figure-8; in the proposed scenario a rapid small-amplitude oscillation induced by a shorter-wavelength laser is superimposed upon this figure-8. Thus, the electron’s momentum is mainly supplied from longer-wavelength laser, while the high-frequency part of the acceleration is given by shorter-wavelength laser. In this way, the harmonics radiated at high frequency from the oscillating electron can be strongly modified by the nonlinear motion initiated by the low frequency, large aL laser resulting in the generation of the harmonics with the photon energy of 4γ2h̵(ωL,short+nωL,long). In this paper, the electron’s kinetics in the two-wavelength laser field and the concomitant emitted radiation spectrum are examined, with numerical illustrations based on a classical Lienard-Wiechert potential formalism provided.
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title: Undulator Radiation Simulation by QUINDI
format: conference proceeding
conference: IPAC 2011
year: 2011
3 authors: D. Schiller | E. Hemsing | J.B. Rosenzweig
abstract: QUINDI, a code developed to simulate coherent emission from bending systems, has been upgraded to include undulators as a beamline element. This approach allows us to better model the radiation produced by a relativistic electron bunch propagating through such a device. Additionally, many new features have been added to the QUINDI post-processor, SpecGUI, which allow the user more sophisticated ways to manipulate and analyze the output from QUINDI.
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title: Gain length fitting formula for free-electron lasers with strong space-charge effects
format: journal article
publisher: Physical Review Accelerators and Beams
year: 2011
3 authors: G. Marcus | E. Hemsing | J.B. Rosenzweig
abstract: We present a power-fit formula, obtained from a variational analysis using three-dimensional free-electron laser theory, for the gain length of a high-gain free-electron laser’s fundamental mode in the presence of diffraction, uncorrelated energy spread, and longitudinal space-charge effects. The approach is inspired by the work of Xie [Nucl. Instrum. Methods Phys. Res., Sect. A 445, 59 (2000)], and provides a useful shortcut for calculating the gain length of the fundamental Gaussian mode of a free-electron laser having strong space-charge effects in the 3D regime. The results derived from analytic theory are in good agreement with detailed numerical particle simulations that also include higher-order space-charge effects, supporting the assumptions made in the theoretical treatment and the variational solutions obtained in the single-mode limit.
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title: Three dimensional analysis of longitudinal plasma oscillations in a thermal relativistic electron beam
format: journal article
publisher: Physics of Plasmas
year: 2011
3 authors: A. Marinelli | E. Hemsing | J.B. Rosenzweig
abstract: In this paper, we develop a three-dimensional kinetic theory of longitudinal plasma oscillations in a relativistic electron beam. Our analysis includes the effects of betatronmotion, finite emittance, and energy spread as well as edge effects due to the finite size of the beam. The consequences of these effects are shown to be of significant interest, as they give rise to several distinct new phenomena. These include an emittance induced anisotropy between backward and forward propagating plasma waves as well as a beatwave effect between plasma and betatronoscillations caused by the coupling of betatronmotion to the transverse structure of the charge perturbation. The experimental implications of these new results and their relevance to the beam and radiation physics of advanced light sources, such as free-electron lasers, are also discussed.
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title: Dielectric Wakefield Acceleration of a Relativistic Electron Beam in a Slab-Symmetric Dielectric Lined Waveguide
format: journal article
publisher: Physical Review Letters
year: 15 June 2012
13 authors: G. Andonian | D. Stratakis | M. Babzien | S. Barber | M. Fedurin | E. Hemsing | K. Kusche | P. Muggli | B. O'Shea | X. Wei | O. Williams | V. Yakimenko | and J.B. Rosenzweig
abstract: We report first evidence of wakefield acceleration of a relativistic electron beam in a dielectric-lined slab-symmetric structure. The high energy tail of a ?60??MeV electron beam was accelerated by ?150??keV in a 2 cm-long, slab-symmetric SiO2 waveguide, with the acceleration or deceleration clearly visible due to the use of a beam with a bifurcated longitudinal distribution that serves to approximate a driver-witness beam pair. This split-bunch distribution is verified by longitudinal reconstruction analysis of the emitted coherent transition radiation. The dielectric waveguide structure is further characterized by spectral analysis of the emitted coherent Cherenkov radiation at THz frequencies, from a single electron bunch, and from a relativistic bunch train with spacing selectively tuned to the second longitudinal mode (TM02). Start-to-end simulation results reproduce aspects of the electron beam bifurcation dynamics, emitted THz radiation properties, and the observation of acceleration in the dielectric-lined, slab-symmetric waveguide.
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title: Generating Optical Orbital Angular Momentum in a High-Gain Free-Electron Laser at the First Harmonic
format: journal article
publisher: Physical Review Letters
year: 22 April 2011
3 authors: E. Hemsing | A. Marinelli | J.B. Rosenzweig
abstract: A scheme to generate intense coherent light that carries orbital angular momentum (OAM) at the fundamental wavelength of an x-ray free-electron laser (FEL) is described. The OAM light is emitted as the dominant mode of the system until saturation provided that the helical microbunching imposed on the electron beam is larger than the shot-noise bunching that leads to self-amplified emission. Operating at the fundamental, this scheme is more efficient than alternate schemes that rely on harmonic emission, and can be applied to x-ray FELs without using external optical mode conversion elements.
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title: Observations of low-aberration plasma lens focusing of relativistic electron beams at the underdense threshold
format: journal article
publisher: Physics of Plasmas
year: 21 July 2010
11 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | N. Barov | P. Piot | R. Fliller | G.M. Kazakevich | J. Santucci | J. Li | R. Tikhoplav
abstract: Focusing of a 15 MeV electron bunch by a plasma lens operated at the threshold of the underdense regime has been demonstrated. The strong, 1.7 cm focal length, plasma lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. It is shown through analytic analysis and simulation that the observed spherical aberration of this underdense lens, when expressed as the fractional departure of the focusing strength from its linear expectation, is ?K/K=0.08�0.04. This is significantly lower than the minimum theoretical value for the spherical aberration of an overdense plasma lens. Parameter scans showing the dependence of focusing performance on beam charge, as well as time resolved measurements of the focused electron bunch, are reported.
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title: Breaking the Attosecond, Angstrom and TV/m Field Barriers with Ultrafast Electron Beams
format: conference proceeding
conference: AAC 2010 14th
year: 2010
17 authors: J.B. Rosenzweig | G. Andonian | P. Bucksbaum | A. Fukasawa | M. Ferrario | M. Hogan | E. Hemsing | P. Krejcik | G. Marcus | A. Marinelli | P. Muggli | P. Musumeci | B. O'Shea | F. O'Shea | C. Pellegrini | D. Schiller | G. Travish
abstract: Recent initiatives at UCLA concerning ultra-short, GeV electron beam generation have been aimed at achieving sub-fs pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This scheme uses very low charge beams, which may allow existing FEL injectors to produce few-100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the Stanford X-ray FEL (LCLS, first of its kind, built with essential UCLA leadership) have produced ~2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments at UCLA in cryogenic undulator technology, to create compact accelerator/undulator systems that can lase below 0.15 Å, or be used to permit 1.5 Å operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator for frontier high energy physics applications. We discuss the experimental issues associated with this initiative.
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title: Short period, high field cryogenic undulator for extreme performance x-ray free electron lasers
format: journal article
publisher: APS
year: 13 July 2010
8 authors: F.H. O'Shea | Gabriel Marcus | J. B. Rosenzweig | Michael Scheer | Johannes Bahrdt | Raphael Weingartner | Andreas Gaupp | Florian Gruner
abstract: Short period, high field undulators can enable short wavelength free electron lasers (FELs) at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. We describe an ongoing initiative to develop such an undulator based on an approach that utilizes novel cryogenic materials. While this effort was begun in the context of extending the photon energy regime of a laser-plasma accelerator based electron source, we consider here implications of its application to sub-fs scenarios in which more conventional injectors are employed. The use of such low-charge, ultrashort beams, which has recently been proposed as a method of obtaining single-spike performance in x-ray FELs, is seen in simulation to give unprecedented beam brightness. This brightness, when considered in tandem with short wavelength, high field undulators, enables extremely high performance FELs. Two examples discussed in this paper illustrate this point well. The first is the use of the SPARX injector at 2.1 GeV with 1 pC of charge to give 8 GW peak power in a single spike at 6.5 � with a photon beam peak brightness greater than 1035??photons/(s?mm2?mrad2??0.1%??BW), which will also reach LCLS wavelengths on the 5th harmonic. The second is the exploitation of the LCLS injector with 0.25 pC, 150 as pulses to lase at 1.5 � using only 4.5 GeV energy; beyond this possibility, we present start-to-end simulations of lasing at unprecedented short wavelength, 0.15 �, using 13.65 GeV LCLS design energy.
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title: A Tapered Dielectric Structure for Laser Acceleration at Low Energy
format: preprint
year:
10 authors: J. McNeur | E. Arab | R. Dusad | Z. Hoyer | J.B. Rosenzweig | G. Travish | N. Vartanian | J. Xu | J. Zhou | R.B. Yoder
abstract: This paper extends the physics of the Micro-Accelerator Platform (MAP), which is in development as an optical structure for laser acceleration of relativistic electrons. The MAP is a resonant, optical-scale, slab-symmetric device that is fabricated from dielectric materials using layer-deposition techniques. For stand-alone applications, low-energy electrons (? ~ 0.3) must be synchronously accelerated to relativistic speeds for injection into the MAP. Even lower energies are desired for other particle species (e.g. protons or muons). In this paper, we present design and simulation studies on a tapered geometry and associated coupling scheme that can produce synchronous acceleration at ? < 1 within a MAP-like structure.
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title: Fabrication of a Laser-Based Microstructure for Particle Acceleration
format: preprint
year:
5 authors: J. Zhou | J. McNeur | J.B. Rosenzweig | G. Travish | R.B. Yoder
abstract: This paper extends the physics of the Micro-Accelerator Platform (MAP), which is in development as an optical structure for laser acceleration of relativistic electrons. The MAP is a resonant, optical-scale, slab-symmetric device that is fabricated from dielectric materials using layer-deposition techniques. For stand-alone applications, low-energy electrons (? ~ 0.3) must be synchronously accelerated to relativistic speeds for injection into the MAP. Even lower energies are desired for other particle species (e.g. protons or muons). In this paper, we present design and simulation studies on a tapered geometry and associated coupling scheme that can produce synchronous acceleration at ? < 1 within a MAP-like structure.
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title: Helical Electron-Beam Microbunching by Harmonic Coupling in a Helical Undulator
format: journal article
publisher: PRL
year: April 29, 2009
7 authors: E. Hemsing | P. Musumeci | S. Reiche | R. Tikhoplav | Agostino Marinelli | J.B. Rosenzweig | A. Gover
abstract: Microbunching of a relativistic electron beam into a helix is examined analytically and in simulation. Helical microbunching is shown to occur naturally when an e beam interacts resonantly at the harmonics of the combined field of a helical magnetic undulator and an axisymmetric input laser beam. This type of interaction is proposed as a method to generate a strongly prebunched e beam for coherent emission of light with orbital angular momentum at virtually any wavelength. The results from the linear microbunching theory show excellent agreement with three-dimensional numerical simulations.
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title: Experimental Demonstration of Emittance Compensation with Velocity Bunching
format: journal article
publisher: Physical Review Letters
year: 5 February 2010
33 authors: M. Ferrario | D. Alesini | A. Bacci | M. Bellaveglia | R. Boni | M. Boscolo | M. Castellano | E. Chiadroni | A. Cianchi | L. Cultrera | G. Di Pirro | L. Ficcadenti | D. Filippetto | V. Fusco | A. Gallo | G. Gatti | L. Giannessi | M. Labat | B. Marchetti | C. Marrelli | M. Migliorati | A. Mostacci | E. Pace | L. Palumbo | M. Quattromini | C. Ronsivalle | A. R. Rossi | J. Rosenzweig | L. Serafini | M. Serluca | B. Spataro | C. Vaccarezza | C. Vicario
abstract: In this Letter we report the first experiments aimed at the simultaneous demonstration of the emittance compensation process and velocity bunching in a high brightness electron source, the SPARC photoinjector in INFN-LNF. While a maximum compression ratio up to a factor 14 has been observed, in a particular case of interest a compression factor of 3, yielding a slice current of 120 A with less than 2 m slice emittance, has been measured. This technique may be crucial in achieving high brightness beams in photoinjectors aiming at optimized performance of short wavelength single-pass free electron lasers or other advanced applications in laser-plasma accelerators.
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title: Observation of coherent terahertz edge radiation from compressed electron beams
format: journal article
publisher: PRSTAB
year: 3 March 2009
9 authors: G. Andonian | A.M. Cook | M. Dunning | E. Hemsing | Gabriel Marcus | A. Murokh | S. Reiche | D. Schiller | J.B. Rosenzweig
abstract: Coherent radiation emitted from a compressed electron bunch as it traverses the sharp edge regions of a magnetic chicane has been investigated at the Brookhaven National Laboratory Accelerator Test Facility. Electron beam measurements using coherent transition radiation interferometry indicate a 100 fs rms bunch accompanied by distinct distortions in energy spectrum due to strong self-fields. These self-fields are manifested in emitted high power THz radiation, which displays signatures of the phenomenon known as coherent edge radiation. Radiation characterization studies undertaken include spectral analysis, far-field intensity distribution, polarization, and dependence on the electron bunch length. The observed aspects of the beam and radiation allow detailed comparisons with start-to-end simulations.
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title: Multiphoton Photoemission from a Copper Cathode Illuminated by Ultrashort Laser Pulses in an rf Photoinjector
format: journal article
publisher: Physical Review Letters
year: 26 February 2010
12 authors: P. Musumeci | L. Cultrera | M. Ferrario | D. Filippetto | G. Gatti | M.S. Gutierrez | J.T. Moody | N. Moore | J.B. Rosenzweig | C.M. Scoby | G. Travish | C. Vicario
abstract: In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 J, 800 nm pulse focused to a 140 m rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.
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title: DEVELOPMENT OF A 1.5+0.5 CELL PHOTOINJECTOR
format: journal article
publisher: PAC 09 Proceedings
year: 2009
6 authors: B. O'Shea | J.B. Rosenzweig | Luigi Faillace | A. Fukasawa | Joshua Moody | Pietro Musumeci
abstract: We present the development and status of a traditional UCLA/BNL/SLAC style 1.5 cell photoinjector with an additional half cell downstream to aid in longitudinal pulse compression. The work presented includes radio frequency design via SuperFish and HFSS as well as beam dynamics simulation using PARMELA. We investigate longitudinal compression of an electron beam in this extra downstream half cell and show shorter final beam lengths at the cost of transverse beam quality, when compared with traditional 1.6 cell systems.
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title: Novel Radio-Frequency Gun Structures For Ultrafast Relativistic Electron Diffraction
format: journal article
publisher: Microscopy and Microanalysis
year: 2009
7 authors: P. Musumeci | L. Faillace | A. Fukasawa | J.T. Moody | B. O'Shea | J.B. Rosenzweig | C.M. Scoby
abstract: Radio-frequency (RF) photoinjector-based relativistic ultrafast electron diffraction (UED) is a promising new technique that has the potential to probe structural changes at the atomic scale with sub-100 fs temporal resolution in a single shot. We analyze the limitations on the temporal and spatial resolution of this technique considering the operating parameters of a standard 1.6 cell RF gun (which is the RF photoinjector used for the first experimental tests of relativistic UED at Stanford Linear Accelerator Center; University of California, Los Angeles; Brookhaven National Laboratory), and study the possibility of employing novel RF structures to circumvent some of these limits.
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title: Observation of Narrow-Band Terahertz Coherent Cherenkov Radiation from a Cylindrical Dielectric-Lined Waveguide
format: journal article
publisher:
year: 2009
6 authors: A. M. Cook | R. Tikhoplav | S. Y. Tochitsky | G. Travish | O. B. Williams | J.B. Rosenzweig
abstract: We report experimental observation of narrow-band coherent Cherenkov radiation driven by a subpico- second electron bunch traveling along the axis of a hollow cylindrical dielectric-lined waveguide. For an appropriate choice of dielectric wall thickness, a short-pulse beam current profile excites only the fundamental mode of the structure, producing energetic pulses in the terahertz range. We resent detailed measurements showing a narrow emission spectrum peaked at 367 3 GHz from a 1 cm long fused silica capillary tube with submillimeter transverse dimensions, closely matching predictions. We demonstrate a 100 GHz shift in the emitted central frequency when the tube wall thickness is changed by 50
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title: Longitudinal phase space characterization of the blow-out regime of rf photoinjector operation
format: journal article
publisher:
year: 2009
5 authors: J.T. Moody | P. Musumeci | M. S. Gutierrez | J.B. Rosenzweig | C. M. Scoby
abstract: Using an experimental scheme based on a vertically deflecting rf deflector and a horizontally dispersing dipole, we characterize the longitudinal phase space of the beam in the blow-out regime at the UCLA Pegasus rf photoinjector. Because of the achievement of unprecedented resolution both in time (50 fs) and energy (1.0 keV), we are able to demonstrate some important properties of the beams created in this regime such as extremely low longitudinal emittance, large temporal energy chirp, and the degrading effects of the cathode image charge in the longitudinal phase space which eventually leads to poorer beam quality. All of these results have been found in good agreement with simulations.
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title: Efficient harmonic microbunching in a 7th-order inverse-free-electron laser interaction
format: journal article
publisher: Physical Review Special Topics- Accelerators and Beams
year: 2009
8 authors: S. Ya. Tochitsky | O.B. Williams | P. Musumeci | C. Sung | D.J. Haberberger | A.M. Cook | J.B. Rosenzweig | C. Joshi
abstract: We have shown that a seventh-order inverse-free-electron laser (IFEL) interaction, where the radiation frequency is the seventh harmonic of the fundamental resonant frequency, can microbunch a beam of relativistic electrons inside an undulator. Using coherent transition radiation (CTR) emitted by the bunched 12.3 MeV beam as a diagnostic, strong microbunching of the beam is inferred from the observation of CTR at the first, second, and third harmonics of the seed 10 m radiation. Threedimensional IFEL simulations show that the observed harmonic ratios can be explained only if transverse spatial distribution of the steepened bunched beam is taken into account.
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title: Coherent transition radiation from a helically microbunched electron beam
format: journal article
publisher:
year: 1 May 2009
2 authors: E. Hemsing | J.B. Rosenzweig
abstract: The coherent transition radiation emitted from an electron beam with higher-order spatial microbunching is analyzed. The characteristic angular and phase dependence can be used to identify the dominant bunching structure of such beams, which can be generated during the harmonic interaction in optical klystron modulators and free-electron lasers, and used as tunable sources of coherent light with orbital angular momentum.
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title: Generation and Measurement of Relativistic Electron Bunches Characterizzed by a Linearly Ramped Current Profile
format: journal article
publisher: PRL
year: May 28, 2008
3 authors: R.J. England | J.B. Rosenzweig | G. Travish
abstract: We report the first successful attempt to generate ultrashort (110 ps) relativistic electron bunches characterized by a ramped longitudinal current profile that rises linearly from head to tail and then falls sharply to zero. Bunches with this type of longitudinal shape may be applied to plasma-based accelerator schemes as an optimized drive beam, and to free-electron lasers as a means of reducing asymmetry in microbunching due to slippage. The scheme used to generate the ramped bunches employs an aniso-chronous dogleg beam line with nonlinear correction elements to compress a beam having an initial positive time-energy chirp. The beam current profile is measured using a deflecting mode cavity, and a pseudoreconstruction of the beams longitudinal phase space distribution is obtained by using this diagnostic with a residual horizontal dispersion after the dogleg.
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title: Breakdown Limits on Gigavolt-per-Meter Electron-Beam-Driven Wakefields in Dielectric Structures
format: journal article
publisher:
year: May 27, 2008
15 authors: M.C. Thompson | H. Badakov | A.M. Cook | J.B. Rosenzweig | R. Tikhoplav | G. Travish | I. Blumenfeld | M.J. Hogan | R. Ischebeck | N. Kirby | R. Siemann | D. Walz | P. Muggli | A. Scott | R.B. Yoder
abstract: First measurements of the breakdown threshold in a dielectric subjected to GV=m wakefields produced by short (30 330 fs), 28.5 GeV electron bunches have been made. Fused silica tubes of 100
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title: Longitudinal dispersion of orbital angular momentum modes in high-gain free-electron lasers
format: journal article
publisher: APS
year: July 30, 2008
4 authors: E. Hemsing | Agostino Marinelli | Sven Reiche | J.B. Rosenzweig
abstract: The physical effects of optical mode dispersion in the electron beam of a free-electron laser are investigated for modes that carry orbital angular momentum. The analysis is performed using a derived equivalence between two different formulations that describe the radiation fields in the linear regime.
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title: Experimental Generation and Characterization of Uniformly Filled Ellipsoidal Electron-Beam Distributions
format: journal article
publisher: PRL
year: 2008
5 authors: P. Musumeci | J.T. Moody | R.J. England | J.B. Rosenzweig | T. Tran
abstract: For 40 years, uniformly filled ellipsoidal beam distributions have been studied theoretically, as they hold the promise of generating self-fields linear in the coordinate offset in all three directions. Recently, a scheme for producing such distributions, based on the strong longitudinal expansion of an initially very short beam under its own space-charge forces, has been proposed. In this Letter we present the experimental demonstration of this scheme, obtained by illuminating the cathode in a rf photogun with an ultrashort laser pulse (
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title: Virtual dielectric waveguide mode description of a high-gain free-electron laser. II. Modeling and numerical simulations
format: journal article
publisher: PRA
year: 2008
3 authors: E. Hemsing | A. Gover | J.B. Rosenzweig
abstract: A high-gain free-electron laser is modeled using an expansion of the radiation field in terms of guided Laguerre-Gaussian modes of a virtual dielectric waveguide E. Hemsing, A. Gover, and J. Rosenzweig, preceding paper, Phys Rev. A 77, 063830 2008 . The radiation profile evolution, power gain, and detuning efficiency characteristics are investigated for seeding with fundamental Gaussian and higher-order Laguerre- Gaussian input modes on a Gaussian e-beam in the collective regime. The full wave evolution solution at different seed radiation injection conditions results in determination of the optimal waist size and waist position of the seed radiation beam for maximum power coupling efficiency. Results for guided mode evolution and power gain are shown to be consistent with simulations performed with the code GENESIS 1.3. The amplification and spontaneous generation of FEL radiation with orbital angular momentum is also considered.
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title: Experimental generation and characterization of uniformly filled ellipsoidal beam distributions
format: journal article
publisher: Physical Review Letters
year: 2008
6 authors: P. Musumeci | M.S. Gutierrez | J.T. Moody | C.M. Scoby | J.B. Rosenzweig | T. Tran
abstract: Recently, a scheme for producing ideal uniformly filled ellipsoidal beam distributions, which depends on the strong longitudinal expansion of an initially very short beam under its own space charge forces, has been demonstrated at the UCLA Pegasus Laboratory. Here we present further work on the characterization of this novel regime of operation of a photoinjector. In particular we study the sensitivity of the generation of the uniformly filled ellipsoidal distribution from the initial transverse laser profile. The ultra-high brightness of the beam created operating in this �blow-out� regime is verified obtaining high quality relativistic electron diffraction patterns from thin Al foils.
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title: Virtual dielectric waveguide mode description of a high-gain free-electron laser. I. Theory
format: journal article
publisher: PRA
year: 2008
3 authors: E. Hemsing | A. Gover | J.B. Rosenzweig
abstract: A set of mode-coupled excitation equations for the slowly growing amplitudes of dielectric waveguide eigenmodes is derived as a description of the electromagnetic signal field of a high-gain free-electron laser FEL, including the effects of longitudinal space charge. This approach of describing the field basis set has notable advantages for FEL analysis in providing an efficient characterization of eigenmodes, and in allowing a clear connection to free-space propagation of the input seeding and output radiation. The formulation describes the entire evolution of the radiation wave through the linear gain regime, prior to the onset of saturation, with arbitrary initial conditions. By virtue of the flexibility in the expansion basis, this technique can be used to find the direct coupling and amplification of a particular mode. A simple transformation converts the derived coupled differential excitation equations into a set of coupled algebraic equations and yields a matrix determinant equation for the FEL eigenmodes. A quadratic index medium is used as a model dielectric waveguide to obtain an expression for the predicted spot size of the dominant system eigenmode, in the approximation that it is a single Gaussian mode.
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title: Single spike operation in SPARC SASE-FEL
format: conference proceeding
conference: EPAC 2008
year: 2008
16 authors: I. Boscolo | F. Castelli | S. Cialdi | V. Petrillo | A. Bacci | L. Serafini | R. Bonifacio | M. Boscolo | M. Ferrario | C. Vaccarezza | L. Giannessi | C. ROnsivalle | L. Palumbo | M. Serluca | J.B. Rosenzweig | S. Reiche
abstract: The single spike operation regime has been analyzed in the case of the SPARC injector and freeelectron-laser. Four different beams at 50 pC are studied, with different production condition and performance.
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title: Status of the Fermi@Elettra Photoinjector
format: conference proceeding
conference: EPAC 2008
year: 2008
21 authors: M. Trovo | L. Badano | S. Biedron | D. Castronovo | F. Cianciosi | P. Craievich | M.D. Danailov | G.DAuria | M. Ferianis | S.V. Milton | G. Penco | L. Pivetta | L. Rumiz | D. Wang | M. Eriksson | D. Kumbaro | F. Lindau | H. Badakov | A. Fukasawa | B. O'Shea | J.B. Rosenzweig
abstract: The new FERMI@Elettra photoinjector is presently undergoing high-power testing and characterization at MAXlab in Lund, Sweden. This effort is a collaboration between Sincrotrone Trieste, MAX-lab and UCLA. The 1.6-cell RF gun cavity and the focusing solenoid were successfully designed and built by the Particle Beam Physics Laboratory at UCLA, delivered to Sincrotrone Trieste at the beginning of 2008, and installed in the linac tunnel at MAX-lab. Use of the MAX-lab facility will allow the FERMI project to progress significantly with the photoinjector while waiting for the completion of the new linac building extension at Sincrotrone Trieste. We report here on the high-power conditioning of the RF cavity and the first beam tests.
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title: Experimental Generation and Characterization of Uniformly Filled Ellipsoidal Beam Distribution
format: conference proceeding
conference: EPAC 2008
year: 2008
6 authors: P. Musumeci | M.S. Gutierrez | J.T. Moody | C.M. Scoby | J.B. Rosenzweig | T. Tran
abstract: Recently, a scheme for producing ideal uniformly filled ellipsoidal beam distributions, which depends on the strong longitudinal expansion of an initially very short beam under its own space charge forces, has been demonstrated at the UCLA Pegasus Laboratory. Here we present further work on the characterization of this novel regime of operation of a photoinjector. In particular we study the sensitivity of the generation of the uniformly filled ellipsoidal distribution from the initial transverse laser profile. The ultra-high brightness of the beam created operating in this blow-out regime is verified obtaining high quality relativistic electron diffraction patterns from thin Al foils.
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title: A Novel Fabrication Technique for the Production of RF Photoinjectors
format: conference proceeding
conference: EPAC 2008
year: 2008
9 authors: P. Frigola | R. Agustsson | S. Boucher | A. Murokh | J.B. Rosenzweig | G. Travish | L. Faillace | D. Cormier | T. Mahale
abstract: Recent developments in Solid Freeform Fabrication (SFF) technology may make it possible to design and produce near netshape copper structures for the next generation of very high duty factor, high gradient radio frequency (RF) photoinjectors. RF and thermal management optimized geometries could be fully realized without the usual constraints and compromises of conventional machining techniques. A photoinjector design incorporating SFF and results from an initial material feasibility study will be reported.
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title: Design and Fabrication of an X-Band traveling wave deflection mode cavity for longitudinal characterization of ultra-short electron beam pulses
format: conference proceeding
conference: EPAC 2008
year: 2008
9 authors: A. Murokh | R. Agustsson | S. Boucher | P. Frigola | J.B. Rosenzweig | J. England | G. Travish | D. Alesini | V. Yakimenko
abstract: An X-band Traveling wave Deflector mode cavity (XTD) has been developed at Radiabeam Technologies to perform longitudinal characterization of the subpicosecond ultra-relativistic electron beams. The device is optimized for the 100 MeV electron beam parameters at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory, and is scalable to higher energies. An XTD is designed to operate at 11.424 GHz, and features short filling time, femtosecond resolution, and a small footprint. RF design, fabrication procedure, and commissioning plans are presented. An experimental program at ATF to utilize the deflector for compressed beam characterization is discussed, including proposed measurements of the phase space filamentation due to non-linear processes in a chicane compressor.
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title: Recent results and future perspectives of the SPARC project
format: conference proceeding
conference: EPAC 2008
year: 2008
77 authors: M. Ferrario | D. Alesini | M. Bellaveglia | R. Boni | M. Boscolo | M. Castellano | E. Chiadroni | A. Clozza | L. Cultrera | G. Di Pirro | A. Drago | A. Esposito | L. Ficcadenti | D. Filippetto | V. Fusco | A. Gallo | G. Gatti | A. Ghigo | B. Marchetti | Agostino Marinelli | C. Marrelli | M. Migliorati | A. Mostacci | E. Pace | L. Palumbo | L. Pellegrino | R. Ricci | U. Rotundo | C. Sanelli | F. Sgamma | B. Spataro | F. Tazzioli | S. Tomassini | C. Vaccarezza | M. Vescovi | C. Vicario | F. Ciocci | G. Dattoli | A. Dipace | a. Doria | G. P. Gallerano | L. Giannessi | E. Giovenale | G. Orlandi | S. Pagnutti | A. Petraia | M. Quattromini | C. Ronsivalle | E. Sabia | I. Spassovsky | V. Surrenti | L. Catani | A. Cianchi | M. Mattioli | M. Petrarca | M. Serluca | A. Bacci | I. Boscolo | F.Broggi | F. Castelli | S. Cialdi | C. De Martinis | D. Giove | C. Maroli | V. Petrillo | A.R. Rossi | L. Serafini | J.B. Rosenzweig | M. E. Couprie | M. Bougeard | B. Carré | D. Garzella | M. Labat | G. Lambert | H. Merdji | P. Salières | O. Tchebakoff
abstract: The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive 500 nm FEL experiments in various configurations, a Thomson backscattering source and a plasma accelerator experiment (these last two ones jointly with the project PLASMONX). The SPARC photoinjector is also the test facility for the recently approved VUV FEL project named SPARX. As a first stage of the commissioning, a complete characterization of the photoinjector has been accomplished with a detailed study of the emittance compensation process downstream the gun-solenoid system: this lead to the first direct experimental demonstration of emittance oscillations in a drift. The second stage of the commissioning, that is currently underway, foresees a detailed analysis of the beam matching with the linac in order to confirm the theoretically prediction of emittance compensation based on the invariant envelope matching and the demonstration of the velocity bunching technique in the linac. SASE and SEEDING experiments are foreseen by the end of the current year. In this paper we report the experimental results obtained so far and the scientific program for the near future.
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title: Simulation of and progress towards a micron-scale laser-powered dielectric electron source
format: conference proceeding
conference: EPAC 2008
year: 2008
5 authors: G. Travish | J.B. Rosenzweig | Jin Xu | R.B. Yoder | S. Boucher
abstract: A dielectric, slab-symmetric structure for generating and accelerating low-energy electrons has been under study for the past two years. The resonant device is driven by a side-coupled laser and is configured to maintain field profiles necessary for synchronous acceleration and focusing of nonrelativistic particles. Intended applications of the structure include the production of radiation for medical treatments, imaging, and industrial uses. Results from 3D simulation of the structure geometry and its resonant properties are presented here.
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title: Quasi-crystalline beam (QCB) formation in strongly accelerating intense electron distributions
format: talk
year: 2008
1 author: J.B. Rosenzweig
abstract: QUASI-CRYSTALLINE BEAM (QCB) FORMATION IN STRONGLY ACCELERATING INTENSE ELECTRON DISTRIBUTIONS Prof. J. Rosenzweig Frascati, LNF, June 12, 2008
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title: High brightness electron beam emittance evolution measurements in an rf photoinjector
format: journal article
publisher: Physical Review Special Topics- Accelerators and Beams
year: 2008
48 authors: A. Cianchi | D. Alesini | A. Bacci | M. Bellaveglia | R. Boni | M. Boscolo | M. Castellano | L. Catani | E. Chiadroni | S. Cialdi | A. Clozzo | L. Cultrera | G. Di Pirro | A. Drago | A. Esposito | M. Ferrario | L. Ficcadenti | D. Filippetto | V. Fusco | A. Gallo | G. Gatti | A. Ghigo | L. Giannessi | C. Ligi | M. Mattioli | M. Migliorati | A. Mostacci | P. Musumeci | E. Pace | L. Palumbo | L. Pellegrino | M. Petrarca | M. Preger | M. Quattromini | R. Ricci | C. Ronsivalle | J.B. Rosenzweig | A.R. Rossi | C. Sanelli | L. Serafini | M. Serio | F. Sgamma | B. Spataro | F. Tazzioli | S. Tomassini | C. Vaccarezza | M. Vescovi | and C. Vicario
abstract: The new generation of linac injectors driving free electron lasers in the self-amplified stimulated emission (SASE-FEL) regime requires high brightness electron beams to generate radiation in the wavelength range from UV to x rays. The choice of the injector working point and its matching to the linac structure are the key factors to meet this requirement. An emittance compensation scheme presently applied in several photoinjectors worldwide is known as the ��Ferrario�� working point. In spite of its great importance there was, so far, no direct measurement of the beam parameters, such as emittance, transverse envelope, and energy spread, in the region downstream the rf gun and the solenoid of a photoinjector to validate the effectiveness of this approach. In order to fully characterize the beam dynamics with this scheme, an innovative beam diagnostic device, the emittance meter, consisting of a movable emittance measurement system, has been designed and built. With the emittance meter, measurements of the main beam parameters in both transverse phase spaces can be performed in a wide range of positions downstream the photoinjector. These measurements help in tuning the injector to optimize the working point and provide an important benchmark for the validation of simulation codes. We report the results of these measurements in the SPARC photoinjector and, in particular, the first experimental evidence of the double minimum in the emittance oscillation, which provides the optimized matching to the SPARC linac.
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title: Direct Measurement of the Double Emittance Minimum in the Beam Dynamics of the Sparc High-Brightness Photoinjector
format: journal article
publisher: Physical Review Letters
year: 6 December 2007
47 authors: M. Ferrario | D. Alesini | A. Bacci | M. Bellaveglia | R. Boni | M. Boscolo | M. Castellano | L. Catani | E. Chiadroni | S. Cialdi | A. Cianchi | A. Clozza | L. Cultrera | G. Di Pirro | A. Drago | A. Esposito | L. Ficcadenti | D. Filippetto | V. Fusco | A. Gallo | G. Gatti | A. Ghigo | L. Giannessi | C. Ligi | M. Mattioli | M. Migliorati | A. Mostacci | P. Musumeci | E. Pace | L. Palumbo | L. Pellegrino | M. Petrarca | M. Quattromini | R. Ricci | C. Ronsivalle | J.B. Rosenzweig | A.R. Rossi | C. Sanelli | L. Serafini | M. Serio | F. Sgamma | B. Spataro | F. Tazzioli | S. Tomassini | C. Vaccarezza | M. Vescovi | C. Vicario
abstract: In this Letter we report the first experimental observation of the double emittance minimum effect in the beam dynamics of high-brightness electron beam generation by photoinjectors; this effect, as predicted by the theory, is crucial in achieving minimum emittance in photoinjectors aiming at producing electron beams for short wavelength single-pass free electron lasers. The experiment described in this Letter was performed at the SPARC photoinjector site, during the first stage of commissioning of the SPARC project. The experiment was made possible by a newly conceived device, called an emittance meter, which allows a detailed and unprecedented study of the emittance compensation process as the beam propagates along the beam pipe.
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title: LASER-POWERED DIELECTRIC STRUCTURE AS A MICRON-SCALE ELECTRON SOURCE
format: preprint
year: 2007
3 authors: J.B. Rosenzweig | G. Travish | R. B. Yoder
abstract: We describe a resonant laser-powered structure, measur- ing 1 mm or less in every dimension, that is capable of generating and accelerating electron beams to low ener- gies ( 1�2 MeV). Like several other recently investigated dielectric-based accelerators, the device is planar and res- onantly excited with a side-coupled laser; however, exten- sive modifications are necessary for synchronous accelera- tion and focusing of nonrelativistic particles. Electrons are generated within the device via a novel ferroelectric-based cathode. The accelerator is constructed from dielectric ma- terial using conventional microfabrication techniques and powered by a 1- m gigawatt laser. The electron beams pro- duced are suitable for a number of existing industrial and medical applications.
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title: MITIGATION OF ELECTRIC BREAKDOWN IN AN RF PHOTOINJECTOR BY REMOVAL OF TUNING RODS IN HIGH-FIELD REGIONS
format: preprint
year: 2007
5 authors: K. Serratto | P. Frigola | J.B. Rosenzweig | M.P. Dunning | A.M. Cook
abstract: The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, the full cell geometry must be changed significantly. We report on a method of accomplishing this, in which we use a mechanical device of custom design to stretch the cavity structure of an existing photoinjector in order to tune the resonant frequency up by over 2 MHz. We present results of testing the modified photoinjector in an RF test bed with both copper and magnesium cathodes, succeeding in putting approximately 8 - 10 MW of RF power into the gun. This is an improvement over the 4 MW routinely achieved in a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory.
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title: DIELECTRIC WAKEFIELD ACCELERATOR EXPERIMENTS AT THE SABER FACILITY
format: preprint
year: 2007
17 authors: G. Travish | H. Badakov | A.M. Cook | J.B. Rosenzweig | R. Tikhoplav | A. Kanareykin | M.C. Thompson | M. K. Berry | I. Blumenfeld | F.J. Decker | M. Hogan | R. Ischebeck | R. Iverson | N. Kirby | R. Siemann | D. Walz | P. Muggli
abstract: Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC Final Focus Test Beam (FFTB), are foreseen to be produced at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of multi-GV/m in plasmas. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 um and 200 um ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in fused silica (with full data analysis still ongoing) [1]. With the construction and commissioning of the SABER facility at SLAC, new experiments would be made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. This collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures.
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title: Chicane Radiation Measurements with a Compressed Electron Beam at the BNL ATF
format: conference proceeding
conference: PAC 2007
year: 2007
12 authors: G. Andonian | R. Agustsson | A.M. Cook | M. Dunning | E. Hemsing | A. Murokh | Sven Reiche | J.B. Rosenzweig | M. Babzien | K. Kusche | R. Malone | V. Yakimenko
abstract: The radiation emitted from a chicane compressor has been studied at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF). Coherent edge radiation (CER) is emitted from a compressed electron beam as it traverses sharp edge regions of a magnet. The compression is accompanied by strong self-fields, which are manifested as distortions in the momentum space called beam bifurcation. Recent measurements indicate that the bunch length is approximately 100 fs rms. The emitted THz chicane radiation displays strong signatures of CER. This paper reports on the experimental characterization and subsequent analysis of the chicane radiation measurements at the BNL ATF with a discussion of diagnostics development and implementation. The characterization includes spectral analysis, far-field intensity distribution, and polarization effects. Experimental data is benchmarked to a custom developed start-to-end simulation suite.
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title: Beam-Driven Dielectric Wakefield Accelerating Structure as a THz Radiation Source
format: preprint
year: 2007
9 authors: A. Kanareykin | O.B. Williams | R. Tikhoplav | A.M. Cook | H. Badakov | J.B. Rosenzweig | G. Travish | M.C. Thompson | R. J. England
abstract: Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerating structure as a source of THz coherent Cerenkov radiation (CCR). For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the device operates in a single-mode regime, producing radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ~50 uJ radiated energy per pulse achievable using the electron beam currently in operation at the Neptune advanced accelerator laboratory at UCLA (~13 MeV beam energy, ~200 um RMS bunch length, ~500 pC bunch charge). Preparations underway for installation of the experiment are discussed.
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title: commissioning of the UCLA Neptune X-Band Deflecting Cavity and Applications to Current Profile Measurement of Ramped Electron Bunches
format: conference proceeding
conference: PAC 2007
year: 2007
5 authors: R. J. England | B. O'Shea | J.B. Rosenzweig | G. Travish | D. Alesini
abstract: A 9-cell standing wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Laboratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid-Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a pi phase advance per cell. At the maximum deflecting voltage of 500 kV, the theoretical resolution limit of the device is 50 fs, although with current beam parameters and a spot size of 460 microns RMS the effective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application: measuring the temporal current profile of ramped electron bunches generated using the Neptune dogleg compressor, and we present the first measurements of the electron beam current profile obtained using the deflecting cavity.
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title: DIELECTRIC WAKEFIELD ACCELERATOR EXPERIMENTS AT THE SABER FACILITY
format: conference proceeding
conference: PAC 2007
year: 2007
17 authors: G. Travish | H. Badakov | A.M. Cook | J.B. Rosenzweig | R. Tikhoplav | A. Kanareykin | M.C. Thompson | M. K. Berry | I. Blumenfeld | F.-J. Decker | M. J. Hogan | R. Ischebeck | R. Iverson | N. Kirby | R. Siemann | D. Walz | P. Muggli
abstract: Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC Final Focus Test Beam (FFTB), are foreseen to be produced at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of multi-GV/m in plasmas. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 um and 200 um ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in fused silica (with full data analysis still ongoing) [1]. With the construction and commissioning of the SABER facility at SLAC, new experiments would be made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. This collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures.
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title: THE UCLA HELICAL PERMANENT-MAGNET INVERSE FREE ELECTRON LASER
format: conference proceeding
conference: PAC 2007
year: 2007
7 authors: R. Tikhoplav | J. Frederico | G. Reed | J.B. Rosenzweig | S. Tochitsky | G. Travish | G. Gatti
abstract: The Inverse Free Electron Laser (IFEL) is capable, in principle, of reaching accelerating gradients of up to 1 GV/m making it a prospective accelerator scheme for linear colliders. The Neptune IFEL at UCLA utilizes a 15 MeV Photoinjector-generated electron beam of 0.5 nC and a CO2 laser with peak energy of up to 100 J, and will be able to accelerate electrons to 100 MeV over an 80 cm long, novel helical permanent-magnet undulator. Past IFELs have been limited in their average accelerating gradient due to the Gouy phase shift caused by tight focusing of the drive laser. Here, laser guiding is implemented via an innovative Open Iris-Loaded Waveguide Structure (OILS) scheme which ensures that the laser mode size and wave front are conserved through the undulator. The results of the first phase of the experiment are discussed in this paper, including the design and construction of a short micro-bunching undulator, testing of the OILS waveresults of corresponding simulations.waveguide to test the coupling by observing a micro- bunching. Then, as a second step, we will build a long waveguide and a tapered undulator (80 cm).
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title: OPTIMUM ELECTRON BUNCH CREATION IN A PHOTOINJECTOR USING SPACE-CHARGE EXPANSION
format: conference proceeding
conference: PAC 2007
year: 2007
16 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | R.J. England | P. Musumeci | M. Bellaveglia | M. Boscolo | L. Catani | A. Cianchi | G. Di Pirro | M. Ferrario | D. Filippetto | G. Gatti | L. Palumbo | C. Vicario | S. Jones
abstract: Recent studies have shown that by illuminating a pho- tocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped electron bunch can be dynamically formed. Linear space- charge fields then exist in all dimensions inside of the bunch, which minimizes emittance growth. Here we study this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. We show that the two processes are com- patible, with simulations indicating that a very high bright- ness beam can be obtained. An initial time-resolved experi- ment has been performed at the SPARC injector in Frascati, involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments at the UCLA Pegasus labo- ratory to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed.
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title: Observation of Multi-GeV Breakdown Thresholds in Dielectric Wakefield Structures
format: conference proceeding
conference: PAC 2007
year: 2007
12 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | M. Hogan | R. Ischebeck | N. Kirby | R. Siemann | D. Walz | P. Muggli | A. Scott | R. Yoder
abstract: An experiment designed to test the breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been completed. In this experiment at the Final Focus Test Beam (FFTB) facility, the 30 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 ?m. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compres- sion of the electron bunch. We observed a sharp increase in optical emissions from the capillaries in the middle part of this surface field range which we believe indicates the transition between sustainable field levels and breakdown. If this initial interpretation is correct, the multi-GV/m sur- faced fields that were sustained equate to on axis accelerat- ing field of several GV/m.
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title: OBSERVATIONS OF UNDERDENSE PLASMA LENS FOCUSING OF RELATIVISTIC ELECTRON BEAMS
format: conference proceeding
conference: PAC 2007
year: 2007
10 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | R. Fliller | G. M. Kazakevich | P. Piot | J. Santucci | J. Li | R. Tikhoplav
abstract: Focusing of a 15 MeV, 19 nC electron bunch by an un- derdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in ex- periments at the Fermilab NICADD Photoinjector Labora- tory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and re- duced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this un- derdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion.
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title: Characterization of Orbital Angular Momentum Modes in FEL Radiation
format: conference proceeding
conference: PAC 2007
year: 2007
5 authors: E. Hemsing | G. Andonian | J.B. Rosenzweig | M. Babzien | V. Yakimenko
abstract: It is well known that Gaussian modes of paraxial light can possess orbital angular momentum (OAM) as a result of a exp( ?il?) azimuthal angular dependence[1]. Recent experiments on the VISA free-electron laser operating as self-amplified spontaneous amplifier (SASE) at ?=840 nm have produced transverse electromagnetic radiation inten- sity patterns that suggest the presence of one or more OAM modes. Though the intensity profiles from VISA are com- pelling, work remains to discern the phase structure since OAM modes are revealed by a characteristic helical phase dependence, with a pathological singularity on axis. Here we discuss current efforts to characterize the mode content of the VISA FEL through experiments, theoretical mod- els, and simulations. Possible methods to generate OAM modes in situ are discussed.
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title: The FINDER Photoinjector
format: conference proceeding
conference: PAC 2007
year: 2007
6 authors: A. Fukasawa | H. Badakov | B. O'Shea | E. Hemsing | J.B. Rosenzweig | S. G. Anderson
abstract: The FINDER photoinjector was developed for the inverse Compton scattering experiment under UCLA- LLNL collaboration. The improvements of this gun from SPARC gun [1, 2] at INFN-LNF (Frascati) and previous UCLA versions of the 1.6 cell S-band photoinjector are detailed here. The gun is designed to have large mode separation to suppress 0 mode excitation which may be a cause of the emittance degradation. In an effort to reduce the RF quadrupole effect the full cell tuners are replaced by vacuum ports. The laser ports are also omitted. Two openings of the solenoid shield are added to top and bottom of it where there were only two openings on the sides. S11 of the cavity was presented. The on-axis electric field was measured by the bead drop method to show the good field balance. The magnetic field in the emittance compensation solenoid was measured and the quadrupole components were derived.
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title: Seeded VISA: A 1064 nm Laser-Seeded FEL Amplifier at the BNL ATF
format: conference proceeding
conference: PAC 2007
year: 2007
7 authors: M. Dunning | G. Andonian | E. Hemsing | S. Reiche | J.B. Rosenzweig | M. Babzien | V. Yakimenko
abstract: An experimental study of a seeded Free Electron Laser (FEL) using the VISA undulator and a Nd:YAG seed laser will be performed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory. The study is motivated by the demand for a short Rayleigh length FEL amplifier at 1 micron to allow for high power transmission with min- imal damage of transport optics. Planned measurements include transverse and longitudinal coherence, angular dis- tribution, and wavelength spectrum of the FEL radiation. The effects of detuning the electron beam energy will be studied, with an emphasis on control of the radiation emis- sion angles and increase of the amplifier efficiency. Results of start-to-end simulations are also presented.
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title: Coherent Cherenkov Radiation as a Temporal Diagnostic for Microbunched Beams
format: conference proceeding
conference: PAC 2007
year: 2007
4 authors: Giancarlo Gatti | A.M. Cook | J.B. Rosenzweig | Rodion Tikhoplav
abstract: Cherenkov radiation of a relativistic e-beam traversing a thin section of aerogel is analized, putting the stress on the coherent contribution due to the intra-beam, transverse and longitudinal structure. The use of this tool as a temporal diagnostic for micro-bunched beams makes possible to improve the amount of collected power at the microbunching frequency several orders of magnitude more respect to the uncoherent Cherenkov contribution. The non-idealities of a real beam are taken in account, and some techniques aimed on enhancing the coherent part of radiation are proposed and analized analitically.
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title: Experimental Characterization of the Transverse Phase Space of a 60-MeV Electron Beam through a Compressor Chicane
format: conference proceeding
conference: PAC 2007
year: 2007
8 authors: F. Zhou | A. Kabel | J.B. Rosenzweig | R. Agustsson | G. Andonian | D. Cline | A. Murokh | V. Yakimenko
abstract: Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12MeV.
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title: Dielectric Wakefield Accelerator Experiments at the Saber Facility
format: conference proceeding
conference: PAC 2007
year: 2007
17 authors: G. Travish | H. Badakov | A.M. Cook | J.B. Rosenzweig | R. Tikhoplav | A. Kanareykin | M.C. Thompson | M.K. Berry | I. Blumenfeld | F.J. Decker | M.J. Hogan | R. Ischebeck | R. Iverson | N. Kirby | R. Siemann | D. Walz | P. Muggli
abstract: Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC Final Focus Test Beam (FFTB), are foreseen to be produced at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of multi-GV/m in plasmas. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 um and 200 um ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in fused silica (with full data analysis still ongoing) [1]. With the construction and commissioning of the SABER facility at SLAC, new experiments would be made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. This collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures.
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title: Observations of Underdense Plasma Lens Focusing of Relativistic Electron Beams
format: conference proceeding
conference: PAC 2007
year: 2007
10 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | R. Fliller | G.M. Kazakevich | P. Piot | J. Santucci | J. Li | R. Tikhoplav
abstract: Focusing of a 15 MeV, 19 nC electron bunch by an un- derdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in ex- periments at the Fermilab NICADD Photoinjector Labora- tory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and re- duced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this un- derdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion.
keywords: pbpl_pub  
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title: Commissioning of the UCLA Neptune X-band Deflecting Cavity and Applications to Current Profile Measurement of Ramped Electron Bunches
format: conference proceeding
conference: PAC 2007
year: 2007
5 authors: R.J. England | B. O'Shea | J.B. Rosenzweig | G. Travish | D. Alesini
abstract: A 9-cell standing-wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Lab- oratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid- Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a ? phase advance per cell. At the maximum deflecting voltage of 530 kV, the theoretical res- olution limit of the device is 50 fs, although with current beam parameters and a RMS spot size of 460 ?m the ef- fective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application of measuring the temporal current profile of ramped electron bunches generated using the Neptune dog- leg compressor, and we present the first measurements of the electron beam current profile obtained using the deflect- ing cavity.
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title: The UCLA Helical Permanent-Magnet Inverse Free Electron Laser
format: conference proceeding
conference: PAC 2007
year: 2007
7 authors: R. Tikhoplav | J. Frederico | G. Reed | J.B. Rosenzweig | S. Tochitsky | G. Travish | G. Gatti
abstract: The Inverse Free Electron Laser (IFEL) is capable, in principle, of reaching accelerating gradients of up to 1 GV/m making it a prospective accelerator scheme for linear colliders. The Neptune IFEL at UCLA utilizes a 15 MeV Photoinjector-generated electron beam of 0.5 nC and a CO2 laser with peak energy of up to 100 J, and will be able to accelerate electrons to 100 MeV over an 80 cm long, novel helical permanent-magnet undulator. Past IFELs have been limited in their average accelerating gradient due to the Gouy phase shift caused by tight focusing of the drive laser. Here, laser guiding is implemented via an innovative Open Iris-Loaded Waveguide Structure (OILS) scheme which ensures that the laser mode size and wave front are conserved through the undulator. The results of the first phase of the experiment are discussed in this paper, including the design and construction of a short micro-bunching undulator, testing of the OILS waveguide, as well as the results of corresponding simulations.
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title: High Average Current Betatrons for Industrial and Security Applications
format: conference proceeding
conference: PAC 2007
year: 2007
8 authors: S. Boucher | R. Agustsson | P. Frigola | A. Murokh | M. Ruelas | F.H. O'Shea | J.B. Rosenzweig | G. Travish
abstract: The fixed-field alternating-gradient (FFAG) betatron has emerged as a viable alternative to RF linacs as a source of high-energy radiation for industrial and security applications. For industrial applications, high average currents at modest relativistic electron beam energies, typically in the 5 to 10 MeV range, are desired for medical product sterilization, food irradiation and materials processing. For security applications, high power x-rays in the 3 to 20 MeV range are needed for rapid screening of cargo containers and vehicles. In a FFAG betatron, high-power output is possible due to high duty factor and fast acceleration cycle: electrons are injected and accelerated in a quasi-CW mode while being confined and focused in the fixed-field alternating- gradient lattice. The beam is accelerated via magnetic induction from a betatron core made with modern low- loss magnetic materials. Here we present the design and status of a prototype FFAG betatron, called the Radiatron, as well as future prospects for these machines.
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title: Beam-driven Dielectric Wakefield Accelerating Structure as a Thz Radiation Source
format: conference proceeding
conference: PAC 2007
year: 2007
9 authors: A.M. Cook | H. Badakov | R.J. England | J.B. Rosenzweig | R. Tikhoplav | G. Travish | O.B. Williams | M.C. Thompson | A. Kanareykin
abstract: Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerat- ing structure as a source of THz coherent Cerenkov radi- ation (CCR). For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the de- vice operates in a single-mode regime, producing radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ?50 ?J radiated energy per pulse achievable using the elec- tron beam currently in operation at the Neptune advanced accelerator laboratory at UCLA ( ?13 MeV beam energy, ?200 ?m RMS bunch length, ?500 pC bunch charge). Preparations underway for installation of the experiment are discussed.
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title: Laser-Powered Dielectric Structure as a Micron-Scale Electron Source
format: conference proceeding
conference: PAC 2007
year: 2007
3 authors: R.B. Yoder | G. Travish | J.B. Rosenzweig
abstract: We describe a resonant laser-powered structure, measur- ing 1 mm or less in every dimension, that is capable of generating and accelerating electron beams to low ener- gies ( ? 1�2 MeV). Like several other recently investigated dielectric-based accelerators, the device is planar and res- onantly excited with a side-coupled laser; however, exten- sive modifications are necessary for synchronous accelera- tion and focusing of nonrelativistic particles. Electrons are generated within the device via a novel ferroelectric-based cathode. The accelerator is constructed from dielectric ma- terial using conventional microfabrication techniques and powered by a 1-?m gigawatt laser. The electron beams pro- duced are suitable for a number of existing industrial and medical applications.
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title: Observation of Multi-GeV Breakdown Thresholds in Dielectric Wakefield Structures
format: conference proceeding
conference: PAC 2007
year: 2007
12 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | M.J. Hogan | R. Ischebeck | N. Kirby | R. Siemann | D. Walz | P. Muggli | A. Scott | R. Yoder
abstract: An experiment designed to test the breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been completed. In this experiment at the Final Focus Test Beam (FFTB) facility, the 28.5 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 ?m. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compres- sion of the electron bunch. We observed a sharp increase in optical emissions from the capillaries in the middle part of this surface field range which we believe indicates the transition between sustainable field levels and breakdown. If this initial interpretation is correct, the multi-GV/m sur- faced fields that were sustained equate to on axis accelerat- ing field of several GV/m.
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title: RF Measurements results of the final brazed SPARC RF Deflector
format: journal article
publisher:
year: 2007
7 authors: L. Ficcadenti | L. Palumbo | A. Mostacci | D. Alesini | C. Vaccarezza | G. Di Pirro | J.B. Rosenzweig
abstract: The longitudinal phase space and the horizontal beam slice emittance measurements of the SPARC 150MeV-lnC electron beam, foresee the use of a RF deflector. he device is a five cells standing wave structure operating on the TM110-like dipole mode at 2.856Ghz and allows reaching a longitudinal resolution of ~12um with 2MW of peak input power. In the paper we illustrate the RF measurements results on the final brazed copper device.
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title: Status of the SPARC-X Project
format: conference proceeding
conference: PAC 2007
year: 2007
97 authors: C. Vaccarezza | D. Alesini | M. Bellaveglia | S. Bertolucci | R. Boni | M. Boscolo | M. Castellano | A. Clozza | L. Cultrera | G. Di Pirro | A. Drago | A. Esposito | M. Ferrario | L. Ficcadenti | D. Filippetto | V. Fusco | A. Gallo | G. Gatti | A. Ghigo | C. Ligi | Agostino Marinelli | M. Migliorati | A. Mostacci | E. Pace | L. Palumbo | L. Pellegrino | M. Preger | R. Ricci | C. Sanelli | M. Serio | F. Sgamma | B. Spataro | A. Stella | F. Tazzioli | M. Vescovi | C. Vicario | F. Ciocci | G. Dattoli | A. Dipace | A. Doria | F. Flora | G.P. Gallerano | L. Giannessi | E. Giovenale | G. Messina | P.L. Ottaviani | S. Pagnutti | G. Parisi | L. Picardi | M. Quattromini | A. Renieri | G. Ronci | C. Ronsivalle | M. Rosetti | E. Sabia | M. Sassi | A. Torre | A. Zucchini | M. Mattioli | D. Pelliccia | L. Catani | E. Chiadroni | A. Cianchi | E. Gabrielli | C. Schaerf | P. Musumeci | M. Petrarca | F. Alessandria | A. Bacci | R. Bonifacio | I. Boscolo | F. Broggi | C. De Martinis | F. Castelli | S. Cialdi | D. Giove | A. Flacco | C. Maroli | V. Petrillo | A.R. Rossi | L. Serafini | A. Perrone | M. Labat | O. Tcherbakoff | G. Lambert | D. Garzella | M. Bougeard | P. Breger | P. Monchicourt | H. Merdji | P. Salie?res | B. Carre? | M. E. Couprie | P. Emma | C. Pellegrini | S. Reiche | J.B. Rosenzweig
abstract: SPARC-X is a two branch project consisting in the SPARC test facility dedicated to the development and test of critical subsystems such as high brightness photoinjector and a modular expandable undulator for SASE-FEL experiments at 500 nm with seeding, and the SPARX facility aiming at generation of high brilliance coherent radiation in the 1.5-13 nm range, based on the achieved expertise. The projects are supported by MIUR (Research Department of Italian Government) and Regione Lazio. SPARC has completed the commissioning phase of the photoinjector in November 2006. The achieved experimental results are here summarized together with the status of the second phase commissioning plans. The SPARX project is based on the generation of ultra high peak brightness electron beams at the energy of 1 and 2 GeV generating radiation in the 1.5-13 nm range. The construction is at the moment planned in two steps starting with a 1 GeV Linac. The project layout including both RF-compression and magnetic chicane techniques has been studied.
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title: The New Photoinjector for the Fermi Project
format: conference proceeding
conference: PAC 2007
year: 2007
14 authors: G. D'Auria | D. Bacescu | L. Badano | F. Cianciosi | P. Craievich | M. Danailov | G. Penco | L. Rumiz | M. Trovo' | A. Turchet | H. Badakov | A. Fukusawa | B. O'Shea | J.B. Rosenzweig
abstract: FERMI@elettra is a single-pass FEL user facility covering the spectral range 100-10 nm. It will be located near the Italian third generation Synchrotron Light Source facility ELETTRA and will make use of the existing 1.0 GeV normal conducting Linac [1]. To obtain the high beam brightness required by the project, the present Linac electron source will be substituted with a photocathode RF gun now under development in the framework of a collaboration between Sincrotrone Trieste (ST) and Particle Beam Physics Laboratory (PBPL) at UCLA. The new gun will use an improved design of the 1.6 cell accelerating structure already developed at PBPL, scaled to 2998 MHz. We expect that the new gun design will allow a beam brightness increase by a factor 3-4 over the older version of the device. Some technical choices of the new design, including the enhancement of the mode separation, removal of the RF tuners, full cell symmetrization to limit the dipole and quadrupole RF field as well as an improved solenoid yoke design for multipole field corrections, will be discussed.
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title: Commissioning of a High-Brightness Photoinjector for Compton Scattering X-Ray Sources
format: conference proceeding
conference: PAC 2007
year: 2007
13 authors: S. G. Anderson | C. P. J. Barty | D. J. Gibson | F. V. Hartemann | M. Messerly | M. Shverdin | C. W. Siders | A. M. Tremaine | H. Badakov | P. Frigola | A. Fukasawa | B. O'Shea | J.B. Rosenzweig
abstract: Compton scattering of intense laser pulses with ultra- relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV ener- gies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free- electron lasers and laser and plasma based advanced accel- erators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scatter- ing experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emit- tance diagnostic development, results of sputtered magne- sium photo-cathode experiments, and UV laser pulse shap- ing are discussed. Initial operation of the photoinjector is described.
keywords: pbpl  
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title: Seeded free-electron and inverse free-electron laser techniques for radiation amplification and electron microbunching in the terahertz range
format: journal article
publisher: Physical Review Letters
year: 22 December 2006
6 authors: C. Sung | S. Ya. Tochitsky | S. Reiche | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: A comprehensive analysis is presented that describes amplification of a seed THz pulse in a single-pass free-electron laser (FEL) driven by a photoinjector. The dynamics of the radiation pulse and the modulated electron beam are modeled using the time-dependent FEL code, GENESIS 1.3. A 10-ps (FWHM) electron beam with a peak current of 50100 A allows amplification of a 1 kWseed pulse in the frequency range 0.53 THz up to 10100 MW power in a relatively compact 2-m long planar undulator. The electron beam driving the FEL is strongly modulated, with some inhomogeneity due to the slippage effect. It is shown that THz microbunching of the electron beam is homogeneous over the entire electron pulse when saturated FEL amplification is utilized at the very entrance of an undulator. This requires seeding of a 30-cm long undulator buncher with a 13 MW of pump power with radiation at the resonant frequency. A narrow-band seed pulse in the THz range needed for these experiments can be generated by frequency mixing of CO2 laser lines in a GaAs nonlinear crystal. Two schemes for producing MW power pulses in seeded FELs are considered in some detail for the beam parameters achievable at the Neptune Laboratory at UCLA: the first uses a waveguide to transport radiation in the 0.53 THz range through a 2-m long FEL amplifier and the second employs high-gain third harmonic generation using the FEL process at 39 THz.
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title: Dielectric Wakefield Accelerating Structure as a Source of Terahertz Coherent Cerenkov Radiation
format: conference proceeding
conference: AAC 2006 12th
year: 2006
8 authors: A.M. Cook | J.B. Rosenzweig | M.C. Thompson | H. Badakov | G. Travish | R. Tikhoplav | O.B. Williams | R. J. England
abstract: We discuss future experimental work proposed to study the performance of a cylindrical dielectric wakefield accelerating structure as a coherent Cerenkov radiation source at the Neptune laboratory at UCLA. The Cerenkov wakefield acceleration experiment carried out recently by UCLA/SLAC/USC, using the ultrashort and high charge beam (Q = 3 nC, RMS bunch length = 20 micron) at the SLAC FFTB, demonstrated electromagnetic wakes at the few GV/m level. The motivation of our prospective experiment is to investigate the operation of a similar scenario using the comparatively long pulse, low charge beam (Q = 0.5 nC, RMS bunch length = 200 micron) at UCLA Neptune. The field amplitude produced in this setup would be one to two orders of magnitude lower, at the few tens to few 100 MV/m level. Such a decelerating field would extract a significant amount of energy from a low-energy beam in a distance on the order of a few centimeters, allowing the use of short dielectric structures. We discuss details of the geometry and composition of the structures to be used in the experiment. We also examine the possibility of a future dedicated facility at UCLA Neptune based on a hybrid photoinjector currently in development. The intrinsic bunch compression capabilities and improved beam parameters (RMS bunch length = 100 micron, Q = 1 nC) of the photoinjector would allow the creation of a high power radiation source in the terahertz regime.
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title: Limits on production of narrow band photons from inverse Compton scattering
format: conference proceeding
conference: AAC 2006 12th
year: 2006
2 authors: J.B. Rosenzweig | O.B. Williams
abstract: In using the inverse Compton scattering (ICS) interaction as a high brilliance, short wavelength radiation source, one collides two beams, one an intense laser, and the other a high charge, short pulse electron beam. In order to maximize the flux of photons from ICS, one must focus both beams strongly, which implies both use of short beams and the existence of large angles in the interaction. One aspect of brilliance is the narrowness of the wavelength band emitted by the source. This paper explores the limits of ICS-based source brilliance based on inherent wavelength broadening effects that arise due to focal angles, laser energy density, and finite laser pulse length effects. It is shown that for a nominal 1% desired bandwidth, that one obtains approximately one scattered photon per electron in a head-on collision geometry
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title: Experiment to Measure Ramped Electron Bunches at the UCLA Neptune Laboratory Using a Transverse Deflecting Cavity
format: conference proceeding
conference: AAC 2006 12th
year: 2006
5 authors: R. J. England | D. Alesini | B. O'Shea | J.B. Rosenzweig | G. Travish
abstract: A proof of principle experiment is underway at the UCLA Neptune laboratory to test the concept of generating linearly ramped relativistic electron bunches (rising in density from head to tail followed by a sharp cutoff) by using a sextupole-corrected dogleg section as a bunch compressor. Bunches with this structure have been predicted to be ideal for use as a plasma wake-field drive beam. The diagnostic being developed to measure the time profile of the beam is an X-Band (9.6 GHz) deflecting cavity. The recently completed cavity is a 9-cell standing wave structure operating in a TM110-like mode, designed to measure the temporal structure of the 2 to 10 ps, 14 MeV electron bunches generated by the Neptune S-band photoinjector and plane-wave transformer (PWT) accelerator beamline, with 50 fs resolution. We discuss the experimental plan for the ramped bunch experiment and present preliminary data related to the tuning and operation of the deflecting cavity.
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title: An Inverse Compton Scattering Radiation Source via Self-Guiding in a Plasma
format: conference proceeding
conference: AAC 2006 12th
year: 2006
2 authors: R. B. Yoder | J.B. Rosenzweig
abstract: In an inverse-Compton scattering source, in which a relativistic electron beam collides with a high-power laser pulse, the x-ray flux produced is proportional to the brightness of the two beams and the size of their overlap region in three-dimensional space. In vacuum, this overlap is limited by the diffraction of the two beams, but the diffraction limit can be overcome by confining both beams in a plasma guiding channel. A dense, bunched electron beam injected into an underdense plasma will self-guide via ``blowout,'' in which the beam head creates a focusing ion channel through which the body of the beam is guided; this same channel can also guides a counterpropagating laser beam. Constraints include the need for long laser wavelength (1 to 10 ?m) and high beam densities. We present a possible configuration for a gamma-ray source using 180� Compton scattering in a uniform plasma, including 2D simulation results. Estimated photon yields are up to a factor of 5 larger than in vacuum scattering, with production of nearly 1010 photons per nanocoulomb of electron beam charge.
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title: Magnetic Chicane Radiation Studies at the BNL ATF
format: conference proceeding
conference: FEL 2006 28th
year: 2006
11 authors: M.Dunning | G. Andonian | A.M. Cook | E. Hemsing | A.Murokh | Sven Reiche | J.B. Rosenzweig | D. Schiller | M. BABZIEN | K. Kusche | V. Yakimenko
abstract: Radiation emitted by relativistic electrons traversing the magnetic field gradients of a chicane bunch compressor has been studied in an attempt to characterize coherent edge radiation (CER). The studies performed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) include frequency spectrum, angular distribution, and polarization measurements. A reconstruction of the longitudinal charge profile from the measured spectrum shows that the bunch has been compressed to approximately 30 ?m FWHM, with a peak current exceeding 1.5 kA. Measurements of radiation from the short pulses are compared to predictions from QUINDI, a new simulation code developed at UCLA to model the radiation.
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title: Optimum Beam Creation In Photoinjectors Using Space-Charge Expansion
format: conference proceeding
conference: FEL 2006 28th
year: 2006
16 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | R. J. England | M. Bellaveglia | M. Boscolo | L. Catani | A. Cianchi | G. Di Pirro | M. Gerrario | D. Filippetto | G. Gatti | P. Musumeci | L. Palumbo | C. Vicario | S. Jones
abstract: It has recently been shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Frascati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed.
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title: RF Design of the UCLA/INFN Hybrid SW/TW Photoinjector
format: conference proceeding
conference:
year: 2006
9 authors: J.B. Rosenzweig | Alessandro Boni | A. Fukasawa | D. Alesini | Massimo Ferrario | Bruno Spataro | Luca Ficcadenti | Andrea Palumbo | B. O'Shea
abstract: With increasing demand for high brightness, low emittance beams for use with freeelectron lasers, Compton scattering systems and wake-field accelerator experiments, stringent requirements have been placed on the design and operation of the 1.6 cell photoinjector. The proposed hybrid photoinjector combines the BNL/UCLA/SLAC style 1.5/1.6 cell standing wave gun with a traveling wave accelerator. Our goal is an injector that meets todays requirements and is scalable in design to meet tomorrows demands: emittances in the region of 1 mm-mrad for higher brightness as well as higher currents. The hybrid photoinjector also offers higher energy operation, enhanced cost effectiveness and better scalability than current designs such as integrated PWT photoinjectors and split gun/accelerating sections. The use of both SW and TW systems allows for higher gradients (Eo = 70 MV/m) in the SW gun for effective capture at lower emittances, while the lower energy acceleration in the TW sections (Eo = 13.5 MV/m) allows generation of higher energy beams which are less sensitive to space charge effects. We note the current results of simulation of beam dynamics, en,x = 3 mm-mrad, an energy spread of 1.5% with beam energies of 21 MeV at currents as high as 1.2 kA. Further we explore the possibilities of scalability to higher frequencies, analysis of coupling design, present cold test preparations and simulated RF analysis of the structure.
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title: Beam compression experiments using the UCLA/ATF compressor
format: conference proceeding
conference: AAC 2006 12th
year: 2006
13 authors: D. Schiller | E. Hemsing | J.B. Rosenzweig | M.P. Dunning | G. Andonian | A. Murokh | A.M. Cook | Sven Reiche | M. Babzien | K. Kusche | V. Yakimenko | L. Palumbo | C. Vicario
abstract: We review recent experimental results from the BNL ATF using the compressor built by UCLA. The measurements discussed include: first observation of short wavelength coherent edge radiation angular/wavelength spectrum and spectrum, sub-100 fsec pulse-length coherent transition autocorrelation measurements, and longitudinal and transverse phase space distortions. Extension of these measurements, as well as those which can be made possible by a new X-band traveling wave deflector being developed in an industrial collaboration, are examined.
keywords: quindi  
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title: Beam Dynamics in a Hybrid Standing Wave-Traveling Wave Photoinjector
format: conference proceeding
conference: AAC 2006 12th
year: 2006
11 authors: J.B. Rosenzweig | D. Alesini | A. Boni | M. Ferrario | L. Ficcadenti | A. Fukusawa | A. Mostacci | B. O'Shea | L. Palumbo | B. Spataro | V. Fusco
abstract: We discuss the dynamics of of a photoinjector beam in a hybrid traveling wave-standing wave photoinjector. With the field profile deduced from electromagnetic simulations, it is seen that the acceleration program induces strong velocity bunching. The beam dynamics in this scenario are explored using UCLA PARMELA. With a solenoid field overlaid on the TW section one may control emittance oscillations during bunching and acceleration. It is seen that the S-band device currently under development at UCLA may produce a 1 nC, 21 MeV, 100 micron rms pulse length beam, with emittance of 3 mm-mrad. Applications of this beam for creating coherent radiation are discussed.
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title: Optimum Beam Creation in Photoinjectors Using Space-Charge Expansion
format: journal article
publisher:
year: 2006
4 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | R.J. England
abstract: It has recently been shown that by illuminating a photo- cathode with an ultra-short laser pulse of appropriate trans- verse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compat- ible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Fras- cati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary ex- periment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measure- ments at high energy based on fs resolution RF sweepers are discussed.
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title: Future FEL Studies at the VISA Experiment in the SASE and Seeded Modes
format: journal article
publisher:
year: 2006
9 authors: G. Andonian | M.P. Dunning | A. Y. Murokh | C. Pellegrini | S. Reiche | J.B. Rosenzweig | M. Babzien | I. Ben-Zvi | V. Yakimenko
abstract: The VISA (Visible to Infrared SASE Amplifier) experiment at BNL (Brookhaven National Laboratory) has previously demonstrated saturation at 840 nm in 2001. Further SASE studies, in 2003, have demonstrated an anomalously large bandwidth spread of the FEL spectrum due to off-angle emissions. This paper disseminates the current and future program of the VISA program at BNL. This includes a study of a seeded FEL, using a 1 micron YAG laser as a seed, and the accompanying diagnostics to characterize the radiation. Diagnostics include the double differential spectrometer, a mode converter to investigate the orbital angular momentum of light in the FEL, and an optical pepper-pot for coherence measurements. As usual, start-to-end simulations are presented.
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title: Nuclear Photo-Science And Applications with Thomson-Radiated Extreme X-Ray (T-Rex) Sources
format: conference proceeding
conference: Linear Accelerator Conference 2006
year: 2006
15 authors: F.V. Hartemann | S.G. Anderson | S.M. Betts | D.J. Gibson | E.P. Hartouni | I. Jovanovic | A.K. Kerman | M. Messerly | D.P. McNabb | J. Pruet | J.B. Rosenzweig | M.Y. Shverdin | C.W. Siders | A.M. Tremaine | C.P.J. Barty
abstract: Recent advances in high brightness rf gun technology, coupled with novel laser systems and architecture have enabled the development of a new class of compact, tunable, monochromatic light sources capable of producing MeV photons with unprecedented brightness. Such new sources rely on Thomson scattering of incident photons produced by a TW-class laser off a bright relativistic electron beam to generate Doppler-upshifted photons in a highly collimated beam. Scaling laws [1] show that a frequency-doubled, 532 nm wavelength, 1 J, 10 ps Fourier transform-limited drive laser pulse interacting with a 250 MeV, 1 nC, 10 ps, 1 mm.mrad normalized emittance, with 0.1% relative energy spread, can yield a 2.24 MeV ?-ray flash with a peak brightness exceeding 1023 photons/[mm2 x mrad2 x s x 0.1% bandwidth]. This number is > 15 orders of magnitude beyond the output of a third-generation synchrotron at the same photon energy. Above ~ 100 keV, the photons can interact with nuclei, and nuclear applications become viable. In this paper, we present a technical overview of T- REX sources and their capabilities, and give a few examples of potential applications of interest.
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title: LASER BEAT-WAVE MICROBUNCHING OF RELATIVISTIC ELECTRON BEAM IN THE THZ RANGE
format: conference proceeding
conference: Linear Accelerator Conference 2006
year: 2006
6 authors: S. Ya. Tochitsky | S. Reiche | C. Sung | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: Laser-driven plasma accelerators have recently demonstrated a ~1GeV energy gain of self-trapped electrons in a several-centimeter-long plasma channel. Potential staging of such devices will require the external injection of an electron beam prebunched on the scale of 1-10 THz into a plasma accelerating structure or plasma LINAC. Seeded FEL/IFEL techniques can be used for modulation of the electron beam longitudinally on the radiation wavelength scale. However, a seed source in this spectral range is not available. At the UCLA Neptune Laboratory a Laser Beat-Wave (LBW) microbunching experiment has begun. The interaction of the electron beam and the LBW results in ponderomotive acceleration and energy modulation on the THz scale. This stage is followed by a ballistic drift of the electrons, where the gained energy modulation is transferred to the beam current modulation. Then the beam is sent into a 33-cm long undulator, where a coherent start-up of THz radiation takes place, and the THz pulse is used for a bunching analysis. The performance of LBW bunching is simulated and analyzed using a 3D FEL code for the parameters of an existing photoinjector and two-wavelength TW CO2 laser system.
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title: Experimental characterization of the transverse phase space of a 60-MeV electron beam through a compressor chicane
format: journal article
publisher:
year: 2006
8 authors: F. Zhou | A. Kabel | J.B. Rosenzweig | R. Agustsson | G. Andonian | D. Cline | A. Murokh | V. Yakimenko
abstract: Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60 MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12 MeV.
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title: STUDY OF THE EFFECT OF MULTIPOLAR COMPONENTS IN THE. SPARC EMITTANCE COMPENSATION GUN SOLENOID
format: conference proceeding
conference: EPAC 2006
year: 2006
11 authors: M. Ferrario | M. Migliorati | P. Musumeci | L. Palumbo | M. Preger | C. Sanelli | G. Dattoli | L. Picardi | M. Quattromini | C. Ronsivalle | J.B. Rosenzweig
abstract: The SPARC photoinjector rf gun requires a solenoid immediately downstream for emittance compensation. The analysis of the measured solenoid magnetic maps shows the existence of multipolar components added to the pure solenoid field. The effect of these added fields on beam dynamics and possible correction schemes have been studied from the theoretical point of view and by numerical calculations based on PARMELA/TREDI codes. An accurate 3D numerical modelization by using CST EM Studio has been done, in order to investigate the source of these multipolar components and to suggest some design modifications aimed to reduce their magnitude. The results of this study are presented here.
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title: The Design of a Hybrid Photoinjector for High Brightness Beam Applications
format: conference proceeding
conference: EPAC 2006
year: 2006
10 authors: D. Alesini | M. Ferrario | V. Fusco | B. Spataro | L. Ficcadenti | A. Mostacci | L. Palumbo | B. O'Shea | J.B. Rosenzweig | G. Travish
abstract: In this paper, we illustrate the electromagnetic and beam dynamics design procedure of a new class of photoinjector, a hybrid standing/traveling wave structure. In this device a standing wave RF gun section is integrated with a downstream traveling wave structure through a coupling cell that feeds simultaneously the two sections. We discuss the advantages in RF and beam performance of the hybrid photoinjector compared to conventional systems. The electromagnetic design has been performed using the 3D electromagnetic code HFSS. Results of beam dynamics simulations in different operating conditions are also discussed.
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title: Development of a Waveguide FEL Seeded in the 1-3 THz Range for Microbunching Experiment at the Neptune Laboratory
format: conference proceeding
conference: AAC 2006 12th
year: 2006
8 authors: C. Sung | S. Ya. Tochitsky | S. Reiche | S. C. Gottschalk | W. D. Kimura | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: IFEL and FEL techniques can be used to modulate an electron beam on the scale of the radiation wavelength. However, the lack of a high power radiation source in the 100-300 ?m range hinders the progress on THz IFEL microbunching. In this paper, we discuss microbunching of an electron beam using a single-pass FEL seeded with a low power THz pulse generated by frequency mixing of CO2 laser lines in a GaAs nonlinear crystal. A narrowband THz seed source is pumped by a dual beam TEA CO2 laser and can be tuned in the 1-3 THz range. The THz radiation is guided through a hollow waveguide inside the planar FEL undulator driven by a photoinjector. By using a time-dependent FEL code GENESIS 1.3, we optimized the undulator parameters and analyzed the dynamics of the modulated electron beam. By using a ~ 8 MeV electron beam with a peak current of 40 A and a ~1kW THz seed with wavelength 200 ?m, the energy modulation up to 1.3% can be achieved in a ~1.8-m long undulator with a constant period of 2.7 cm. At present, the THz seed source is built and fully characterized. The results of transmission measurements for THz waveguides are also discussed.
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title: Observation of Coherent Edge Radiation Emitted by a 100 Femtosecond Compressed Electron Beam
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2006
14 authors: G. Andonian | M. Dunning | E. Hemsing | J.B. Rosenzweig | A. M. Cook | A. Murokh | S. Reiche | M. Babzien | I. Ben-Zvi | K. Kusche | V. Yakimenko | D. Alesini | L. Palumbo | C. Vicario
abstract: A chicane compressor developed by UCLA for the production of ultra-short, 60 MeV electron beams at the Brookhaven National Laboratory Accelerator Test Facility has been commissioned, and initial beam physics experiments have been performed. These measurements have established the compression of electron beams to the 100 femtosecond (1 kA peak current) regime, via coherent transition radiation (CTR) based measurements. Investigations of coherent edge radiation (CER) include signatures that differentiate it from coherent synchrotron radiation (CSR), such as polarization and far-field angular distribution. Additionally, the radiation wavelength spectrum is determined from autocorrelation measurements. Radiation properties are compared to detailed start-to-end simulations derived from PARMELA and QUINDI (a Lienard-Wiechert code developed at UCLA). Plans for future experiments which further explore the observed wavelength spectra are presented.
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title: Ultra-high gradient dielectric wakefield accelerator experiments
format: conference proceeding
conference: AAC 2006 12th
year: 2006
12 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | M. Hogan | R. Ischebeck | N. Kirby | R. Siemann | D. Walz | P. Muggli | A. Scott | R. Yoder
abstract: Ultra-high gradient dielectric wakefield accelerators are a potential option for a linear collider afterburner since they are immune to the ion collapse and electron/positron asymmetry problems implicit in a plasma based afterburner. The first phase of an experiment to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range has been completed. The experiment took advantage of the unique SLAC FFTB electron beam and its ultra-short pulse lengths and high currents (e.g., ?z = 20 ?m at Q = 3 nC). The FFTB electron beam was successfully focused down and sent through short lengths of fused silica capillary tubing (ID = 200 ?m / OD = 325 ?m). The pulse length of the electron beam was varied to produce a range of electric fields between 2 and 20 GV/m at the inner surface of the dielectric tubes. We observed a sharp increase in optical emissions from the capillaries in the middle part of this surface field range which we believe indicates the transition between sustainable field levels and breakdown. If this initial interpretation is correct, the surfaced fields that were sustained equate to on axis accelerating field of several GV/m. In future experiments being developed for the SLAC SABER and BNL ATF we plan to use the coherent Cerenkov radiation emitted from the capillary tube as a field strength diagnostic and demonstrate GV/m range particle energy gain.
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title: Electron Beam-laser Interaction near the Cathode in a High Brightness Photoinjector
format: conference proceeding
conference: EPAC 2006
year: 2006
4 authors: M. Ferrario | G. Gatti | L. Serafini | J.B. Rosenzweig
abstract: The production of high charge short bunches in a high brightness photoinjector requires laser pulses driving the cathode with GW range peak power on a mm spot size. The resulting transverse electric field experienced by the electron beam near the cathode is of the order of 200-500 MV/m, well in excess of a typical RF accelerating field of 50-100 MV/m. We present here a preliminary study of the resultant beam dynamics. Simulations including the electron beam-laser interaction have been performed with the code HOMDYN taking into account the superposition of incident and reflected laser pulses as well as space charge fields. Under this conditions the emittance degradation is negligible, as predicted by analytical methods, but a longitudinal charge modulation occurs on the scale of the laser wavelength, in case of oblique incidence, driven by the longitudinal component of the laser field. Charge modulation is transformed into energy modulation via the space charge field, which may produce enhanced microbunching effects when the beam is further compressed in a magnetic chicane.
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title: Status of the SPARX FEL Project
format: conference proceeding
conference: EPAC 2006
year: 2006
67 authors: C.Vaccarezza | D.Alesini | M.Bellaveglia | S.Bertolucci | M.E Biagini | R.Boni | M.Boscolo | M.Castellano | A.Clozza | L.Cultrera | G.Di Pirro | A.Drago | A.Esposito | M.Ferrario | D.Filippetto | V.Fusco | A.Gallo | A.Ghigo | S.Guiducci | M.Migliorati | L.Palumbo | L.Pellegrino | M.Preger | C.Sanelli | M.Serio | F.Sgamma | B.Spataro | A.Stella | F.Tazzioli | M.Vescovi | C.Vicario | F. Ciocci | G.Dattoli | A.Doria | F.Flora | G.Gallerano | L.Giannessi | E.Giovenale | G.Messina | P.L. Ottaviani | G.Parisi | L.Picardi | M.Quattromini | A.Renieri | C. Ronsivalle | S.Cialdi | C.Maroli | V.Petrillo | M. Rome | L.Serafini | L.Catani | E.Chiadroni | A. Cianchi | C.Schaerf | P.Musumeci | F.Alessandria | A.Bacci | F.Broggi | C.De Martinis | D.Giove | M.Mauri | L. Ficcadenti | M.Mattioli | A.Mostacci | P.Emma | S.Reiche | J.B. Rosenzweig
abstract: The SPARX project consists in an X-ray-FEL facility jointly supported by MIUR (Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and Rome University Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1 and 2 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5�6 nm and 6�1.5 nm, at 1 GeV and 2 GeV respectively, both in SASE and SEEDED FEL configurations. A hybrid scheme of RF and magnetic compression will be adopted, based on the expertise achieved at the SPARC high brightness photoinjector presently under commissioning at Frascati INFN-LNF Laboratories [1,2]. The use of superconducting and exotic undulator sections will be also exploited. In this paper we report the progress of the collaboration together with start to end simulation results based on a combined scheme of RF compression techniques.
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title: Status of the SPARC Photoinjector
format: conference proceeding
conference: Linear Accelerator Conference 2006
year: 2006
69 authors: D. Alesini | M. Bellaveglia | S. Bertolucci | R. Boni | M. Boscolo | M. Castellano | A. Clozza | L. Cultrera | G. Di Pirro | A. Drago | A. Esposito | M. Ferrario | L. Ficcadenti | D. Filippetto | V. Fusco | G. Gatti | A. Gallo | A. Ghigo | M. Incurvati | C. Ligi | F. Marcellini | M. Migliorati | A. Mostacci | L. Palumbo | L. Pellegrino | M. Preger | R. Ricci | C. Sanelli | M. Serio | F. Sgamma | B. Spataro | A. Stecchi | A. Stella | F. Tazzioli | C. Vaccarezza | M. Vescovi | C. Vicario | F. Alessandria | A. Bacci | I. Boscolo | F. Broggi | S.Cialdi | C. DeMartinis | D. Giove | C. Maroli | M. Mauri | V. Petrillo | M. Rome | A. R. Rossi | L. Serafini | D. Levi | M. Mattioli | P. Musumeci | G. Medici | D. Pelliccia | M. Petrarca | L. Catani | E. Chiadroni | A. Cianchi | E. Gabrielli | S. Tazzari | A. Perrone | L. Giannessi | L. Picardi | M. Quattromini | C. Ronsivalle | J.B. Rosenzweig | G. Travish | S. Reiche
abstract: The SPARC Project is starting the commissioning of its photo-injector. RF gun, RF sources, RF network and control, power supplies, emittance meter, beam diagnostics and control to measure the RF gun beam have been installed. The photocathode drive laser has been characterized in terms of pulse shape and quality. We will report also about first tests made on RF gun and on the emittance meter device. Additional R&D on X-band and S-band structures for velocity bunching are in progress, as well as studies on new photocathode materials. We will also discuss studies on solenoid field defects, beam based alignments and exotic electron bunch production via blow-out of short laser pulses.
keywords: pbpl  
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title: Simulations, Diagnostics and Recent Results of the VISA II Experiment
format: conference proceeding
conference: FEL 2005 27th
year: August 2005
17 authors: G. Andonian | A. Murokh | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | G. Travish | M. Babzien | I. Ben-Zvi | V. Litvinenko | V. Yakimenko | I. Boscolo | S. Cialdi | A. Flacco | M. Ferrario | L. Palumbo | C. Vicario | J. Huang
abstract: The VISA II experiment entails the use of a chirped electron beam to drive a high gain SASE FEL. Sextupoles are implemented to correct the longitudinal aberrations affecting the high energy spread chirped beam during transport to the undulator. The output radiation is diagnosed with a modified frequency resolved optical gating (FROG) technique. The double differential energy spectrum is measured with a pair of slits and a set of gratings. In this paper, we report on start-to-end simulations, radiation diagnostics, as well as initial experimental results. Technical considerations for future experimental methods are also addressed.
keywords: pbpl  
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title: Pulsed-laser nonlinear Thomson scattering for general scattering geometries
format: journal article
publisher: Physical Review E
year: 23 November 2005
3 authors: G. A. Krafft | A. Doyuran | J.B. Rosenzweig
abstract: In a recent paper it has been shown that single electron Thomson backscatter calculations can be performed including the effects of pulsed high intensity lasers. In this paper we present a more detailed treatment of the problem and present results for more general scattering geometries. In particular, we present new results for 90 Thomson scattering. Such geometries have been increasingly studied as x-ray sources of short-pulse radiation. Also, we present a clearer physical basis for these different cases.
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title: Mitigation of RF Gun Breakdown by Removal of Tuning Rods in High Field Regions
format: conference proceeding
conference: PAC 2007
year: 2007
5 authors: A.M. Cook | M.P. Dunning | J.B. Rosenzweig | K. Serratto | P. Frigola
abstract: The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, one must change the full cell geometry significantly. We have investigated a method for accomplishing this, in which we stretch the gun structure to tune the resonant frequency up by over 2 MHz. We constructed a device to perform this stretching and tested the modified photoinjector in an RF test bed. We succeeded in putting approximately 8.4 MW of RF power into the gun, an improvement over the 4 MW routinely achieved with a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory. Recent results in testing this gun with a magnesium cathode insert are reported as well.
keywords: pbpl  
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title: PRELIMINARY RESULTS FROM THE UCLA/SLAC ULTRA-HIGH GRADIENT CERENKOV WAKEFIELD ACCELERATOR EXPERIMENT
format: conference proceeding
conference: Erice 2005
year: 2006
12 authors: M.C. Thompson | H. BADAKOV | J.B. Rosenzweig | G. Travish | M. Hogan | R. Ischebeck | N. Kirby | P. Muggli | A. Scott | R. Siemann | D. Walz | R. Yoder
abstract: The first phase of an experiment to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range has been completed. This experiment takes advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., ?z = 20 ?m at Q = 3 nC). The FFTB electron beam has been successfully focused down and sent through varying lengths of fused silica capillary tubing with two different sizes: ID = 200 ?m / OD = 325 ?m and ID = 100 ?m / OD = 325 ?m. The pulse length of the electron beam was varied in the range 20 ?m < ?z < 100 ?m which produced a range of electric fields between 2 and 20 GV/m at the inner surface of the dielectric tubes. We observed a sharp increase in optical emissions from the capillaries in the middle part of this surface field range which we believe indicates the transition between sustainable field levels and breakdown. If this initial interpretation is correct, the surfaced fields that were sustained equate to on axis accelerating field of several GV/m. In future experiments we plan to collect and measure coherent Cerenkov radiation emitted from the capillary tube to gain more information about the strength of the accelerating fields.
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title: The LCLS Single-shot Relative Bunch Length Monitor System
format: conference proceeding
conference: Erice 2005
year: 2006
4 authors: Sven Reiche | M. Dunning | G. Travish | J.B. Rosenzweig
abstract: The Particle Beam Physics Lab (PBPL) at UCLA is developing a single-shot relative bunch length monitor system for the Linac Coherent Light Source (LCLS) X-ray Free Electron Laser at SLAC. To ensure high-quality lasing, feedback systems are needed. The bunch length monitor system will be a crucial part of the linac longitudinal feedback system, which is necessary to keep the final peak beam current stable. The system will consist of two multi-channel single-shot grating polychromators, one after each bunch compressor, and will use the coherent synchrotron radiation (CSR) or coherent edge radiation (CER) from bunch compressor chicane dipole magnets. Details of the system will be presented, and the system will be compared to alternatives. Plans for testing and integration into the LCLS beamline will be presented as well.
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title: EXPERIMENTAL TESTING OF DYNAMICALLY OPTIMIZED PHOTOELECTRON BEAMS
format: conference proceeding
conference: Erice 2005
year: 2006
16 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | R. J. England | P. Musumeci | M. Bellaveglia | M. Boscolo | L. Catani | A. Cianchi | G. Di Pirro | M. Ferrario | D. Filipetto | G. Gatti | L. Palumbo | L. Serafini | C. Vicario
abstract: We discuss the design of and initial results from an experiment in space-charge dominated beam dynamics which explores a new regime of high-brightness electron beam generation at the SPARC (located at INFN-LNF, Frascati) photoinjector. The scheme under study employs the natural tendency in intense electron beams to configure themselves to produce a uniform density, giving a nearly ideal beam from the viewpoint of space charge-induced emittance. The experiments are aimed at testing the marriage of this idea with a related concept, emittance compensation, We show that the existing infrastructure at SPARC is nearly ideal for the proposed tests, and that this new regime of operating photoinjector may be the preferred method of obtaining highest brightness beams with lower energy spread. We discuss the design of the experiment, including developing of a novel time-dependent, aerogel-based imaging system. This system has been installed at SPARC, and first evidence for nearly uniformly filled ellipsoidal charge distributions recorded.
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title: RESULTS FROM THE UCLA/FNPL UNDERDENSE PLASMA LENS EXPERIMENT
format: conference proceeding
conference: Erice 2005
year: 2006
11 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | H. Edwards | R. Fliller | G. M. Kazakevich | P. Piot | J. Santucci | J. Li | R. Tikhoplav
abstract: A gaussian underdense plasma lens with peak density 5 x 1012 cm?3 and a full width half maximum (FWHM) length of 2.2 cm has been used to focus a relativistic electron beam. This plasma lens is equivalent in strength to a quadrupole magnet with a 150 T/m field gradient. The lens focused a 15 MeV, 16 nC electron beam with initial dimensions ?x,y ? 650 ?m and ?z ? 6.5 mm onto an optical transition radiation (OTR) screen ?2 cm downstream of the lens. The average transverse area of the plasma focused electron beam was typically demagnified by a factor of 23. The evolution of the beam envelope in the area near the beam waist was measured for both round beams and asymmetric beams with x:y aspect ratios as large as 1:5. The light from the OTR screen in the round beam case was also imaged into a streak camera in order to directly measure the correlation between z and ? within the beam.
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title: Higher harmonic inverse free-electron laser interaction
format: journal article
publisher: Physical Review E
year: 2005
3 authors: P. Musumeci | C. Pellegrini | J.B. Rosenzweig
abstract: We expand the theory of the inverse free electron laser IFEL interaction to include the possibility of energy exchange that takes place when relativistic particles traversing an undulator interact with an electromagnetic wave of a frequency that is a harmonic of the fundamental wiggler resonant frequency. We derive the coupling coefficients as a function of the IFEL parameters for all harmonics, both odd and even. The theory is supported by simulation results obtained with a three-dimensional Lorentz equation solver code. Comparisons are made between the results of theory and simulations, and the recent UCLA IFEL experimental results where higher harmonic IFEL interaction was observed.
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title: Side-Coupled Slab-Symmetric Structure for High-Gradient Acceleration using Terahertz Power
format: journal article
publisher: PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS
year: 2005
2 authors: R. B. Yoder | J.B. Rosenzweig
abstract: A slab-symmetric dielectric-loaded accelerator structure, consisting of a vacuum gap between dielectric-lined conducting walls, is described. The device is resonantly excited by an external drive laser which is side coupled into the acceleration region; a novel coupling scheme, which consists of an array of narrow, equally spaced slots in the upper structure boundary, is presented and analyzed in detail. This structure partakes of the advantages of earlier slab-symmetric optical acceleration proposals, but will use a terahertz-frequency external radiation source ( 340 m), allowing realistic electron beams to be used in a proof-of-principle experiment. Two- and three-dimensional electromagnetic simulations are used to verify the mode patterns and study the effects of the couplers, including time-dependent calculations of the filling of the structure and particle-in-cell computations of the beam wakefields. Details of the resonance are found to be highly sensitive to the coupling slot geometry: the presence of the couplers can lead to frequency detuning, changes in the field breakdown limits and overall Q factor, and distortions of the field pattern. Beam wakefields are enhanced by the presence of the slots, but found to have no significant effect on the beam transport. The resonant accelerating fields, which are nearly constant along the short transverse direction, are found to have between 10 and 15 times the amplitude of the driving radiation, with only a small ( < 10%) admixture of other nonaccelerating modes. Field gradients are computed to be near 100 MV=m when the structure is driven with 100MWof terahertz laser power. Possible manufacturing methods for a prototype device are discussed.
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title: Creation of plasma density transitions short compared to the plasma skin-depth
format: journal article
publisher: REVIEW OF SCIENTIFIC INSTRUMENTS
year: 2005
3 authors: M.C. Thompson | J.B. Rosenzweig | G. Travish
abstract: A plasma based electron beam source apparatus is described which creates a plasma with two distinct density regions separated by a transition which is shorter than the plasma skin depth kp^−1 of either region. This sharp density modulation is achieved by using a perforated stainless steel screen to filter half of a diffusing plasma column. A simple physical model predicts that the length of the plasma density transition will vary with the distance from the screen. For a weakly magnetized plasma, the transition length will be twice the distance, on a line normal to the screen plane, from the screen edge to the location where the transition is measured. The plasma column is generated using an argon discharge plasma source. It has a peak density of approximately 3.53 X 10^13 cm^−3 and a full width half maximum width of 5 cm. The discharge source utilizes a 7.5 cm diameter LaB6 disk cathode heated to 1300
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title: Recent Results from and Future Plans for the VISA II SASE FEL
format: conference proceeding
conference: PAC 2005
year: 2005
19 authors: G. Andonian | R. Agustsson | P. Frigola | A. Murokh | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | G. Travish | M. BABZIEN | I. Ben-Zvi | V. Litvinenko | V. Yakimenko | I. Boscolo | S. Cialdi | A. Flacco | M. Ferrario | L. Palumbo | C. Vicario | J. Huang
abstract: The VISA II (Visible to Infrared SASE Amplifier) project, a consequent experiment to the succesful VISA enterprise, entails the use of a chirped electron beam to drive a high gain SASE FEL. The resulting ultra-short pulses will be characterized using an advanced FROG (Frequency Resolved Optical Gating) technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole corrections, the resulting high gain lasing, and computational analysis are briefly reported.
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title: Transverse phase space coupling due to quadrupole errors in the SPARC photoinjector
format: talk
year: 2005
1 author: J.B. Rosenzweig
abstract:
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title: Production of High Harmonic X-ray Radiation from Non-linear Thomson Scattering at LLNL PLEIADES
format: conference proceeding
conference: PAC 2005
year: 2005
11 authors: J. Lim | A. Doyuran | P. Frigola | G. Travish | J.B. Rosenzweig | S. Anderson | S. Betts | J. Crane | D. Gibson | F. Hartemann | A. Tremaine
abstract: We describe an experiment for production of high harmonic x-ray radiation from Thomson backscattering of an ultra-short high power density laser by a relativistic electron beam at the PLEIADES facility at LLNL. In this scenario, electrons execute a ``figure-8'' motion under the influence of the high-intensity laser field, where the constant characterizing the field strength is expected to exceed unity: $a_{L}=eE_{L}/m_{e}c\omega_{L}\geq1$. With large $a_{L}$ this motion produces high harmonic x-ray radiation and significant broadening of the spectral peaks. This paper is intended to give a layout of the PLEIADES experiment, along with progress towards experimental goals.
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title: High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser
format: preprint
year: 2005
16 authors: P. Musumeci | S. Boucher | A. Doyuran | R. J. England | C. Pellegrini | J.B. Rosenzweig | G. Travish | R. B. Yoder | S. Ya. Tochitsky | C. E. Clayton | C. Joshi | J. E. Ralph | C. Sung | S. Tolmachev | A. A. Varfolomeev | T. Yarovoi
abstract: Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an Inverse-Free- Electron-Laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and �eld amplitude. The Rayleigh range of the laser, � 1.8 cm, is much shorter than the undulator length yielding a di�raction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the �rst half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.
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title: RF AND MAGNETIC MEASUREMENTS ON THE SPARC PHOTOINJECTOR AND SOLENOID AT UCLA
format: conference proceeding
conference: PAC 2005
year: 2005
8 authors: J.B. Rosenzweig | A.M. Cook | M.P. Dunning | P. Frigola | G. Travish | C. Sanelli | F. Tazzioli | D. T. Palmer
abstract: The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center. Comparisons between measurements and the predictions of design codes are made.
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title: Observation of Anomalously Large Spectral Bandwidth in a High Gain Self-amplified Spontaneous Emission Free-Electron Laser
format: preprint
year: 2005
14 authors: G. Andonian | A. Murokh | J.B. Rosenzweig | R. Agustsson | M. Babzien | I. Ben-Zvi | Pedro Frigola | J. Huang | L. Palumbo | C. Pellegrini | Sven Reiche | G. Travish | C. Vicario | V. Yakimenko
abstract: Observation of ultra-wide bandwidth, up to a full width of 15%, high-gain operation of a self-amplified spontaneous emission free election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (~ 1.7%) emitted from the accelerator. Because of non-linear pulse compression during beam transport, a short, high current pulse with strong mismatch errors is injected into the undulator, bringing about high FEL gain. Start-end simulations reproduce key features of the measured results, and provide insight into mechanisms, such as angular spread in both emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum.
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title: Proposed continuous wave energy recovery operation of an x-ray free electron laser
format: journal article
publisher: Physical Review Special Topics - Accelerators and Beams
year: 2005
17 authors: J. Sekutowicz | S.A. Bogacz | D. Douglas | P. Kneisel | G.P. Williams | M. Ferrario | I. Ben-Zvi | J. Rose | J. Smedley | Srinivasan-Rao, T. | L. Serafini | W.D. Moller | B. .Petersen | D. Proch | S. Simrock | P. Colestock | J.B. Rosenzweig
abstract: Commissioning of two large coherent light facilities (XFELs) at SLAC and DESY should begin in 2008 and 2011, respectively. In this paper we look further into the future, hoping to answer, in a very preliminary way, two questions. First: What will the next generation of XFEL facilities look like? Believing that superconducting technology offers advantages such as high quality beams with highly populated bunches, the possibility of energy recovery and higher overall efficiency than warm technology, we focus this preliminary study on the superconducting option. From this belief the second question arises: What modifications in superconducting technology and in the machine design are needed, as compared to the present DESY XFEL, and what kind of research and development program should be proposed to arrive in the next few years at a technically feasible solution with even higher brilliance and increased overall conversion of ac power to photon beam power? In this paper we will very often refer to and profit from the DESY XFEL design, acknowledging its many technically innovative solutions.
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title: Side-coupled slab-symmetric structure for high-gradient acceleration using terahertz power
format: journal article
publisher: Physical Review Special Topics - Accelerators and Beams
year: 2005
2 authors: R. B. Yoder | J.B. Rosenzweig
abstract: A slab-symmetric dielectric-loaded accelerator structure, consisting of a vacuum gap between dielectric-lined conducting walls, is described. The device is resonantly excited by an external drive laser which is side coupled into the acceleration region; a novel coupling scheme, which consists of an array of narrow, equally spaced slots in the upper structure boundary, is presented and analyzed in detail. This structure partakes of the advantages of earlier slab-symmetric optical acceleration proposals, but will use a terahertz-frequency external radiation source ( 340 m), allowing realistic electron beams to be used in a proof-of-principle experiment. Two- and three-dimensional electromagnetic simulations are used to verify the mode patterns and study the effects of the couplers, including time-dependent calculations of the filling of the structure and particle-in-cell computations of the beam wakefields. Details of the resonance are found to be highly sensitive to the coupling slot geometry: the presence of the couplers can lead to frequency detuning, changes in the field breakdown limits and overall Q factor, and distortions of the field pattern. Beam wakefields are enhanced by the presence of the slots, but found to have no significant effect on the beam transport. The resonant accelerating fields, which are nearly constant along the short transverse direction, are found to have between 10 and 15 times the amplitude of the driving radiation, with only a small ( < 10%) admixture of other nonaccelerating modes. Field gradients are computed to be near 100 MV=m when the structure is driven with 100MWof terahertz laser power. Possible manufacturing methods for a prototype device are discussed.
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title: Recent Results from and Future Plans for the VISA II SASE FEL
format: preprint
year: 2005
19 authors: G. Andonian | R. Agustsson | Pedro Frigola | A. Murokh | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | G. Travish | M. BABZIEN | I. Ben-Zvi | V. Litvinenko | V. Yakimenko | I. Boscolo | S. Cialdi | A. Flacco | M. Ferrario | L. Palumbo | C. Vicario | J. Huang
abstract: The VISA II (Visible to Infrared SASE Amplifier) project, a consequent experiment to the succesful VISA enterprise, entails the use of a chirped electron beam to drive a high gain SASE FEL. The resulting ultra-short pulses will be characterized using an advanced FROG (Frequency Resolved Optical Gating)technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole corrections, the resulting high gain lasing, and computational analysis are briefly reported.
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title: X-Band Dipole Mode Deflecting Cavity for the UCLA Neptune Beamline
format: conference proceeding
conference: PAC 2005
year: 2005
5 authors: R. J. England | B. O'Shea | J.B. Rosenzweig | G. Travish | D. Alesini
abstract: We report progress on the design and construction of a nine-cell cavity operating in a TM110-like dipole mode for use as a temporal diagnostic of the 14 MeV, 300 pC electron bunches generated at the UCLA Neptune Laboratory linear accelerator, with an anticipated temporal resolution of 50 fs at a peak input power of 50 kW. The cavity is a center-fed standing-wave pi-mode structure, operating at 9.6 GHz, and incorporating a knife-edge and gasket assembly which minimizes the need for brazing or welding. Results of initial RF testing of the prototype cavity are discussed and compared with simulation results obtained using the commercial code HFSS.
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title: Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system
format: journal article
publisher: Physical Review Special Topics - Accelerators and Beams
year: 2005
9 authors: J. K. Lim | P. Frigola | G. Travish | J.B. Rosenzweig | S. Anderson | W. J. Brown | J.S. Jacob | C.L. Robbins | A.M. Tremaine
abstract: Advanced high-brightness beam applicaitons such as inverse-Compton scattering (ICS) depend on achieving of ultra-small spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing-systems using high field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560 T/m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication and experimental procedure in creating ultra-small beams at PLEIADES.
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title: Observation of Anomalously Large Spectral Bandwidth in a High-Gain Self-Amplified Spontaneous Emission Free Elctron Laser
format: journal article
publisher: Physical Review Letters
year: 2005
14 authors: G. Andonian | A. Murokh | J.B. Rosenzweig | R. Agustsson | M. BABZIEN | I. Ben-Zvi | P. Frigola | J.Y. Huang | L. Palumbo | C. Pellegrini | Sven Reiche | G. Travish | C. Vicario | V. Yakimenko
abstract: Observation of ultrawide bandwidth, up to 15% full-width, high-gain operation of a self-amplified spontaneous emission free-election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (E=E  1:7%) emitted from the accelerator. Because of nonlinear pulse compression during transport, a short, high current bunch with strong mismatch errors is injected into the undulator, giving high FEL gain. Start-to-end simulations reproduce key features of the measurements and provide insight into mechanisms, such as angular spread in emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum.
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title: Velocity bunching of high-brightness electron beams
format: journal article
publisher: Physical Review Special Topics - Accelerators and Beams
year: 2005
11 authors: S. Anderson | P. Musumeci | J.B. Rosenzweig | W. J. Brown | R. J. England | M. Ferrario | J. S. Jacob | M.C. Thompson | G. Travish | A.M. Tremaine | R. Yoder
abstract: Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modernhigh brightness photoinjector sources. This tool is familiar from earlier schemes implemented for bunching dc electron sources, but presents peculiar challenges when applied to high current, low emittance beams from photoinjectors. The main difficulty foreseen is control of emittance oscillations in the beam in this scheme, which can be naturally considered as an extension of the emittance compensation process at moderate energies. This paper presents two scenarios in which velocity bunching, combined with emittance control, is to play a role in nascent projects. The first is termed ballistic bunching, where the changing of relative particle velocities and positions occur in distinct regions, a short high gradient linac, and a drift length. This scenario is discussed in the context of the proposed ORION photoinjector. Simulations are used to explore the relationship between the degree of bunching, and the emittance compensation process. Experimental measurements performed at the UCLA Neptune Laboratory of the surprisingly robust bunching process, as well as accompanying deleterious transverse effects, are presented. An unanticipated mechanism for emittance growth in bends for highly momentum chirped beam was identified and studied in these experiments. The second scenario may be designated as phase space rotation, and corresponds closely to the recent proposal of Ferrario and Serafini. Its implementation for the compression of the electron beam pulse length in the PLEIADES inverse Compton scattering (ICS) experiment at LLNL is discussed. It is shown in simulations that optimum compression may be obtained by manipulation of the phases in low gradient traveling wave accelerator sections. Measurements of the bunching and emittance control achieved in such an implementation at PLEIADES, as well as aspects of the use of velocity-bunched beam directly in ICS experiments, are presented.
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title: Emittance compensation with dynamically optimized photoelectron beam profiles
format: journal article
publisher: Nuclear Instruments and Methods in Physics Research A
year: 2005
4 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | M. Ferrario
abstract: Much of the theory and experimentation concerning creation of a high-brightness electron beam from a photocathode, and then applying emittance compensation techniques, assumes that one must strive for a uniform density electron beam, having a cylindrical shape. On the other hand, this shape has large nonlinearities in the space-charge field profiles near the beam
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title: Effects of Ion Motion in Intense Beam-Driven Plasma Wakefield Accelerators
format: journal article
publisher: Physical Review Letters
year: 2005
5 authors: J.B. Rosenzweig | A.M. Cook | A. Scott | M.C. Thompson | R. B. Yoder
abstract: Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear collider have included intense electron beams with densities many times in excess of the plasma density. The beams electric fields expel the plasma electrons from the beam path to many beam radii in this regime. We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA collider scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are presented. Implications of ion motion on the feasibility of the PWFA-based colliders are discussed.
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title: A Coherent Compton Backscattering High Gain FEL Using an X-Band Microwave Undulator
format: conference proceeding
conference: FEL 2005 27th
year: 2005
6 authors: S. Tantawi | V. Dolgashev | C. Nantista | C. Pellegrini | J.B. Rosenzweig | G. Travish
abstract: High power microwave sources at X-Band, delivering 400 to 500 of megawatts for about 400 ns, have been recently developed. These sources can power a microwave undulator with short period and large gap, and can be used in short wavelength FELs reaching the nm region at a beam energy of about 1 GeV. We present here an experiment designed to demonstrate that microwave undulators have the field quality needed for high gain FELs. compensate RF power losses, it might be convenient to have an open waveguide geometry, as will be discussed later in the paper. However the initial FEL calculations are based on a circular cross-section waveguide. The undulator is powered by two transverse electric modes, shifted in the time phase by
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title: Investigation of X-Ray Harmonics in the Polarized Nonlinear Inverse Compton Scattering Experiment at UCLA
format: conference proceeding
conference: FEL 2005 27th
year: 2005
8 authors: A. Doyuran | O. Williams | R.J. England | C. Joshi | J. Lim | J.B. Rosenzweig | S. Tochitsky | G. Travish
abstract: An Inverse Compton Scattering (ICS) experiment, which will investigate nonlinear properties of scattering utilizing a terawatt CO2 laser system with various polarizations, is ongoing at the UCLA Neptune Laboratory. When the normalized amplitude of the incident laser's vector potential ao is larger than unity the scattering occurs in the nonlinear region; therefore, higher harmonics are also produced. ICS can be used, e.g., for a polarized positron source by striking a thin target (such as tungsten) with the polarized X-rays. As such, it is critical to demonstrate the production of polarized scattered photons and to investigate the ICS process as it enters the nonlinear regime. We present the description of the experimental set up and equipment utilized, including diagnostics for electron and photon beam detection. We present the current status of the experiment. electron beam focusing and recollimating systems consist of 5 equal strength and length PMQs each, set up as a modified FF-DD-F triplet. The high power CO2 laser is focused by an off-axis parabolic mirror with a 12.7 cm diameter and 17 cm focal length. Since the divergence of the scattered photons is quite large (-I/, where 28) it is necessary to place the detector (soft X-ray camera and/or micro-channel plate) very close to the IP. This requires bending the electron beam immediately after the recollimating PMQ system, in a very short bending radius. To this end, we have designed and built a permanent magnet dipole (PMD) with a -60 mm bending radius for this purpose. Table 1: Electron and Laser Beam Parameters
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title: Ultra-High Density Electron Beams for Beam Radiation and Beam Plasma Interaction
format: conference proceeding
conference: PAC 2005
year: 2005
11 authors: G. Anderson | W.J. Brown | D. J. Gibson | F.V. Hartemann | J.S. Jacob | A.M. Tremaine | J. K. Lim | P. Frigola | P. Musumeci | J.B. Rosenzweig | G. Travish
abstract: Current and future applications of high brightness electron beams, which include advanced accelerators such as the plasma wake-field accelerator (PWFA) and beam radiation interactions such as inverse-Compton scattering (ICS), require both transverse and longitudinal beam sizes on the order of tens of microns. Ultra-high density beams may be produced at moderate energy (50 MeV) by compression and subsequent strong focusing of low emittance, photoinjector sources. We describe the implementation of this method used at the PLEIADES ICS x-ray source in which the photoinjector-generated beam has been compressed to 300 fsec duration using the velocity bunching technique and focused to 20 um rms size using an extremely high gradient, permanent magnet quadrupole (PMQ) focusing system.
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title: Terahertz IFEL/FEL Microbunching for Plasma Beatwave Accelerators
format: journal article
publisher:
year: 2005
9 authors: C. Sung | S. Ya. Tochitsky | J. Ralph | P. Musumeci | S. Reiche | C. Clayton | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: In order to obtain monoenergetic acceleration of electrons, phase-locked injection using electron microbunches shorter than the accelerating structure is necessary. For a laser-driven plasma beatwave accelerator experiment, we propose to microbunch the electrons by interaction with terahertz (THz) radiation in an undulator via two mechanisms� Free Electron Laser (FEL) and Inverse Free Electron Laser (IFEL). Since the high power FIR radiation will be generated via difference frequency mixing in GaAs by the same CO2 beatwave used to drive the plasma wave, electrons could be phase-locked and pre-bunched into a series of microbunches separated with the same periodicity. Here we examine the criteria for undulator design and present simulation results for both IFEL and FEL approaches. Using different CO2 laser lines, electrons can be microbunched with different periodicity 300 �100 ?m suitable for injection into plasma densities in the range 1016 � 1017 cm-3, respectively. The requirements on the THz radiation power and the electron beam qualities are also discussed.
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title: High Energy gain IFEL at the UCLA Neptune Laboratory
format: journal article
publisher:
year: 2005
16 authors: P. Musumeci | S. Ya. Tochitsky | S. Boucher | A. Doyuran | R. J. England | C. Joshi | C. Pellegrini | J. Ralph | J.B. Rosenzweig | C. Sung | G. Travish | R. Yoder | A. A. Varfolomeev | S. Tolmachev | A. Varfolomeev Jr. | T. Yarovoi
abstract: We report on the observation of energy gain in excess of 20MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5MeV electron beam is injected in a 50cm longundulator strongly tapered both in period and field amplitude. A CO210.6?m laser with power > 400GW is used as the IFEL driver. The Rayleigh range of the laser(?1.8cm)is shorter than the undulator length so that the interaction is diffraction dominated. Few per cent of the injected particles are trapped instable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometer. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. Anenergygradientof>70MeVisinferred. In these cond section of the undulator higher harmonic IFEL interaction is observed.
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title: Production of femtosecond pulses and micron beam spots for high brightness electron beam applications
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2005
9 authors: S. G. Anderson | D. J. Gibson | F. V. Hartemann | J. S. Jacob | A. M. Tremaine | J. K. Lim | P. Frigola | J.B. Rosenzweig | G. Travish
abstract:
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title: Feasibility Study of a Laser Beat-Wave Seeded THz FEL at the Neptune Laboratory
format: conference proceeding
conference: PAC 2005
year: 2005
6 authors: S. Reiche | C. Joshi | C. Pellegrini | J.B. Rosenzweig | S. Tochitsky | G. Shvets
abstract: Free-Electron Laser in the THz range can be used to generate high output power radiation or to modulate the electron beam longitudinally on the radiation wavelength scale. Microbunching on the scale of 1-5 THz is of partic- ular importance for potential phase-locking of a modulated electron beam to a laser-driven plasma accelerating struc- ture. However the lack of a seeding source for the FEL at this spectral range limits operation to a SASE FEL only, which denies a subpicosecond synchronization of the cur- rent modulation or radiation with an external laser source. One possibility to overcome this problem is to seed the FEL with two external laser beams, which difference (beat- wave) frequency is matched to the resonant FEL frequency in the THz range. In this presentation we study feasibility of an experiment on laser beat-wave injection in the THz FEL considered at the UCLA Neptune Laboratory, where both a high brightness photoinjector and a two-wavelength, TW-class CO2 laser system exist. By incorporating the energy modulation of the electron beam by the pondero- motive force of the beat-wave in a modified version of the time-dependent FEL code Genesis 1.3, the performance of a FEL at Neptune is simulated and analyzed.
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title: HIgh Energy, High Brightness X-Rays Produced by Compton Back Scattering at the Livermore PLEIADES facility
format: conference proceeding
conference: PAC 2005
year: 2005
11 authors: A. M. Tremaine | S. G. Anderson | S. Betts | J. Crane | J. Gibson | F. V. Hartemann | J. S. Jacob | P. Frigola | J. Lim | J.B. Rosenzweig | G. Travish
abstract: PLEIADES (Picosecond Laser Electron Interaction for the Dynamic Evaluation of Structures) produces tunable 30-140 keV x-rays with 0.3-5 ps pulse lengths and up to 10^7 photons/pulse by colliding a high brightness electron beam with a high power laser. The electron beam is created by an rf photo-injector system, accelerated by a 120 MeV linac, and focused to 20 ?m with novel permanent magnet quadrupoles. To produce Compton back scattered x-rays, the electron bunch is overlapped with a Ti:Sapphire laser that delivers 500 mJ, 100 fs, pulses to the interaction point. K-edge radiography at 115 keV on Uranium has verified the angle correlated energy spectrum inherent in Compton scattering and high-energy tunability of the Livermore source. Current upgrades to the facility will allow laser pumping of targets synchronized to the x-ray source enabling dynamic diffraction and time-resolved studies of high Z materials. Near future plans include extending the radiation energies to >400 keV, allowing for nuclear fluorescence studies of materials.
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title: The UCLA/FNPL Time Resolved Underdense Plasma Lens Experiment
format: conference proceeding
conference: PAC 2005
year: 2005
11 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | H. Edwards | R. Fliller | G. M. Kazakevich | P. Piot | J. Santucci | J. Li | R. Tikhoplav
abstract: A gaussian underdense plasma lens with peak density 5 � 1012cm-3and a full width half maximum (FWHM) length of 2.2 cm has been used to focus a relativistic electron beam. This plasma lens has a focusing strength equivalent to a quadrupole magnet with a 150 T/m field gradient. The lens focused a 15 MeV, 16 nC electron beam with initial dimensions ?r= 500 ?m and ?z= 5 mm onto an optical transition radiation (OTR) screen 2 cm downstream of the lens. The average transverse area of the plasma focused electron beam was typically demagnified by a factor of 22. The light from the OTR screen was imaged into a streak camera in order to directly measure the correlation between z and ?rwithin the beam.
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title: Experimental Characterization of 4-D Transverse Phase-Space of a Compressed Beam
format: conference proceeding
conference: PAC 2005
year: 2005
8 authors: F. Zhou | R. Agustsson | G. Andonian | D. Cline | A. Murokh | J.B. Rosenzweig | I. Ben-Zvi | V. Yakimenko
abstract: Coherent synchrotron radiation (CSR) may severely deteriorate electron beam qualities, such as distortion of energy spectrum and transverse phase-space in the bending plane when the beam transports through a magnetic bunch compressor. Recently some laboratories conducted some investigations on CSR effects but mostly focused on the measurements of emittance growth and energy spread and or/ energy loss. However, these parameters may not completely represent a fully compressed beam because its phase spaces may be severely distorted and thus some information may be lost if only these basic parameters are used. It is preferred to reconstruct six-dimensional phase spaces of a compressed beam using tomographic techniques in order to fully understand a beam affected by CSR effects. This report will focus on the four-dimensional transverse phase-space tomographic measurements for a fully compressed beam at 60-MeV energy. Its experimental characterizations at different beam parameters are preliminarily examined.
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title: Production of Terahertz Seed Radiation for FEL/IFEL Microbunchers for Second Generation Plasma Beatwave Experiments at Neptune
format: conference proceeding
conference: PAC 2005
year: 2005
5 authors: J. E. Ralph | S. Ya. Tochitsky | C. Sung | C. Joshi | J.B. Rosenzweig
abstract: To achieve phase locked injection of short electron bunches in a plasma beatwave accelerator, the Neptune Laboratory will utilize microbunching in an FEL or IFEL system. These systems require terahertz (THz) seed radiation on the order of 10 kW for the FEL and 10 MW for the IFEL bunchers. We report results of experiments on THz generation using nonlinear frequency mixing of CO2 laser lines in GaAs. A two-wavelength laser beam was split and sent onto a 2.5 cm long GaAs crystal cut for noncollinear phase matching. Low power measurements achieved ~1 W of 340 ?m radiation using 200 ns CO2 pump pulses with wavelengths 10.3?m and 10.6?m. We also demonstrated tunability of difference frequency radiation, producing 240?m by mixing two different CO2 laser lines. By going to shorter laser pulses and higher intensities, we were able to increase the conversion efficiency while decreasing the surface damage threshold. Using 200ps pulses we produced ~2 MW of 340 ?m radiation. Future studies in this area will focus on developing large diameter Quasi-Phase matched structures for production of high power THz radiation using collinear two frequency radiation.
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title: High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser
format: journal article
publisher: Physical Review Letters
year: 20 April 2005
17 authors: P. Musumeci | S. Ya. Tochitsky | S. Boucher | C. Clayton | A. Doyuran | R. J. England | C. Joshi | C. Pellegrini | J. E. Ralph | J.B. Rosenzweig | C. Sung | Tolmachev, S. | G. Travish | A. A. Varfolomeev | A. A. Varfolomeev | T. Yarovoi | R. B. Yoder
abstract: Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-freeelectron-laser (IFEL) accelerator experiment. A 14.5 MeVelectron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, 1:8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV=m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.
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title: Optimization and beam dynamics of a superconducting radio-frequency gu
format: journal article
publisher: Nuclear Instruments and Methods in Physics Research A
year:
5 authors: M. Ferrario | W. D. Moeller | J.B. Rosenzweig | J. Sekutowicz | G. Travish
abstract: Recent advances in superconducting radio-frequency (RF) technology and a better understanding of RF photoinjector design optimization make it possible to propose a specific design for a superconducting RF gun that can simultaneously produce both ultra-high peak brightness and high average current. Such a device is a critical component of next generation X-ray sources, such as self-amplified spontaneous emission free-electron lasers (SASE FEL) and energy recovery linac-based systems. The design presented in this paper is scaled from the present state-of-the-art normal conducting RF photoinjector that has been studied in the context of the linac coherent light source and SPARC SASE FEL injection schemes. Issues specific to the superconducing RF photoinjector, such as accelerating gradient limit, RF cavity and cryostat design, and compatibility with magnetic focusing and laser excitation of a photocathode are discussed.
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title: Sextupole Correction of the Longitudinal Transport of Relativistic Beams in Dispersionless Translating Sections
format: journal article
publisher: Physical Review Special Topics: Accelerators and Beams
year:
6 authors: R. J. England | J.B. Rosenzweig | G. Andonian | P. Musumeci | G. Travish | R. Yoder
abstract: We examine the use of sextupole magnets to correct nonlinearities in the longitudinal phase space transformation of a relativistic beam of charged particles in a dispersionless translating section, or dogleg. Through heuristic analytical arguments and examples derived from recent experimental endeavors and augmented by simulations using the particle tracking codes PARMELA and ELEGANT, sextupole corrections are found to be potentially useful in facilitating the use of such structures for beam compression or for shaping the current profile of the beam, by manipulation of the second-order longitudinal dispersion (or T566). Recent experimental evidence of the use of sextupoles to manipulate second-order horizontal and longitudinal dispersion of the beam is presented. The theoretical and experimental results indicate that these manipulations could be used to create an electron bunch with a current profile having a long ramp followed by a sharp cut-off, which is optimal for driving large amplitude wake fields in a plasma wake field accelerator.
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title: Very High Energy Gain at the Neptune Inverse Free Electron Laser Experiment
format: journal article
publisher: AIP Conference Proceedings
year: Dec 2004
16 authors: P. Musumeci | S. Ya. Tochitsky | S. Boucher | A. Doyuran | R. J. England | C. Joshi | C. Pellegrini | J. Ralph | J.B. Rosenzweig | C. Sung | S. Tolmachev | G. Travish | A. A. Varfolomeev | A. Varfolomeev Jr. | T. Yarovoi | R. Yoder
abstract: We report the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in an undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 m laser with power larger than 400 GW. The Rayleigh range of the laser, ~ 1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured by a magnetic spectrometer. Three-dimensional simulations, in good agreement with the measured electron energy spectrum, indicate that most of the acceleration occurs in the first 25 cm of the undulator, corresponding to an energy gradient larger than 70 MeV/m. The measured energy spectrum also indicates that higher harmonic Inverse Free Electron Laser interaction takes place in the second section of the undulator.
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title: The Effects of Ion Motion in Very Intense Beam-driven Plasma Wakefield Accelerators
format: journal article
publisher: Physical Review Letters
year: 2004
4 authors: J.B. Rosenzweig | A.M. Cook | M.C. Thompson | R.B. Yoder
abstract: Recent proposals for using plasma wakefield accelerators in the blowout regime as a component of a linear collider have included very intense driver and accelerating beams, which have densities many times in excess of the ambient plasma density. The electric fields of these beams are widely known to be large enough to completely expel plasma electrons from the beam path; the expelled electrons often attain relativistic velocities in the process. We examine here another aspect of this high-beam density scenario: the motion of ions. In the lowest order analysis, for both cylindrically symmetric and
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title: An Optimal Design for a THz Dielectric-Loaded Slab-Symmetric Accelerator
format: conference proceeding
conference: AAC 2004 11th
year: 2004
2 authors: R.B. Yoder | J.B. Rosenzweig
abstract: A slab-symmetric dielectric-loaded accelerator structure, consisting of a vacuum gap between dielectric-lined conducting walls, is analyzed theoretically and computationally. The device is to be resonantly excited by an external laser source of wavelength 340
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title: Creation of plasma density transitions short compared to the plasma skin depth
format: preprint
year: 2004
3 authors: M.C. Thompson | J.B. Rosenzweig | G. Travish
abstract: A plasma based electron beam source apparatus is described which creates a plasma with two distinct density regions separated by a transition which is shorter than the plasma skin depth $k^{-1}_{p}$ of either region. This sharp density modulation is achieved by using a perforated stainless steel screen to filter half of a diffusing plasma column. A simple physical model predicts that the length of the plasma density transition will vary with the distance from the screen. For a weakly magnetized plasma, the transition length will be twice the distance, on a line normal to the screen plane, from the screen edge to the location where the transition is measured. The plasma column is generated using an argon discharge plasma source. It has a peak density of approximately 3.5 x 10$^{13}$ cm$^{-3}$ and a FWHM width of 5 cm. The discharge source utilizes a 7.5 cm diameter LaB$_{6}$ disc cathode heated to $1300^{\circ}$ C using a graphite heater. The plasma column is filtered with a 78 $\mu$m thick stainless steel sheet with 152 $\mu$m holes and 21\% open area. Plasma density transitions with lengths between 0.74$k^{-1}_{p}$ and 0.95$k^{-1}_{p}$ were measured.
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title: Enhanced Acceleration of Injected Electrons in a Laser Beatwave Induced Plasma Channel
format: preprint
year: 2004
10 authors: S. Ya. Tochitsky | R. Narang | C. V. Filip | P. Musumeci | C. E. Clayton | R. B. Yoder | K. A. Marsh | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: Enhanced energy gain of externally injected electrons by a ~3-cm long, high-gradient relativistic plasma wave (RPW) is demonstrated. Using a CO2 laser-beatwave of duration longer than the ion motion time across the laser spot size, a laser self-guiding process is initiated in a plasma channel. Guiding compensates for ionization-induced defocusing (IID) creating a longer plasma, which extends the interaction length between electrons and the RPW. In contrast to a maximum energy gain of 10 MeV when IID is dominant, the electrons gain up to 38 MeV energy in a laser beatwave induced plasma channel. PACS: 52.35Mw, 52.38Hb, 52.38Kd
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title: Plasma density transition trapping as a possible high-brightness electron beam source
format: journal article
publisher: PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS
year: 2004
3 authors: M.C. Thompson | J.B. Rosenzweig | Suk, H.
abstract: Plasma density transition trapping is a recently proposed self-injection scheme for plasma wakefield accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wakefield. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional particle-in-cell simulations show that these parameters can be optimized by manipulating the plasma density profile.We also develop, and support with simulations, a set of scaling laws that predicts how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness > 5 x 10^14 A/(mrad)^2. A proof-of principle transition trapping experiment is planned for the near future. The proposed experiment is described in detail.
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title: An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB
format: conference proceeding
conference: AAC 2004 11th
year: 2004
7 authors: J.B. Rosenzweig | S. Hoover | M. Hogan | P. Muggli | M.C. Thompson | G. Travish | R. Yoder
abstract: The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, ?z= 20 ?m) at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cerenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few 100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields.
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title: Calculation of Coherent Radiation from Ultra-short Electron Beams Using a Li
format: journal article
publisher: AIP
year: 2004
6 authors: A. Flacco | M. Fairchild | Sven Reiche | J.B. Rosenzweig | L. Giannessi | M. Quattromini
abstract: The coherent radiation emitted by electrons in high brightness beam-based experiments is important from the viewpoints of both radiation source development, and the understanding and diagnosing the basic physical processes important in beam manipulations at high intensity. While much theoretical work has been developed to aid in calculating aspects of this class of radiation, these methods do not often produce accurate information concerning the experimentally relevant aspects of the radiation. At UCLA, we are particularly interested in coherent synchrotron radiation and the related phenomena of coherent edge radiation, in the context of a fs-beam chicane compression experiment at the BNL ATF. To analyze this and related problems,we have developed aprogramthat acts as an extension to the Li
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title: Status of the UCLA/NICADD Plasma Density Transition Trapping Experiment
format: preprint
year: 2004
8 authors: M.C. Thompson | J.B. Rosenzweig | G. Travish | N. Barov | H. Edwards | P. Piot | J. Santucci | R. Tikhoplav
abstract: Plasma density transition trapping is a recently proposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. This paper recounts the first attempt to demonstrate density transition trapping experimentally. The goal of the experiment is to capture a ∼ 100 pC, 1.5 MeV beam with 4% rms energy spread out of a 2.5x10^13 cm^−3 peak density plasma using a 6nC, 14 MeV drive beam. The first experimental run occurred at the Fermilab NICADD Photoinjector Laboratory (FNPL) between January and May 2004. While several key objectives were achieved, we were unable to achieve the drive beam parameters necessary for the experiment due to technical problems. We are in the process of resolving these problems in preparation for a second experimental run.
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title: A Helical Undulator Wave-guide Inverse Free-Electron Laser
format: conference proceeding
conference: AAC 2004 11th
year: 2004
8 authors: J.B. Rosenzweig | N. Bodzin | P. Frigola | C. Joshi | P. Musumeci | C. Pellegrini | S. Tochitsky | G. Travish
abstract: With recent success in high gradient, high-energy gain IFEL experiments at the UCLA Neptune Laboratory, future experiments are now being contemplated. The Neptune IFEL was designed to use a tightly focused, highly diffracting, near-TW peak power 10 micron laser. This choice of laser focusing, driven by power-handling limitations of the optics near the interaction region, led to design and use of a very complex undulator, and to sensitivity to both laser misalignment and focusing errors. As these effects limited the performance of the IFEL experiment, a next generation experiment at Neptune has been studied which avoids the use of a highly diffractive laser beam through use of a waveguide. We discuss here the choice of low-loss waveguide, guided mode characteristics and likely power limitations. We also examine a preferred undulator design, which is chosen to be helical in order to maximize the acceleration achieved for a given power. With the limitations of these laser and undulator choices in mind, we show the expected performance of the IFEL using 1D simulations. Three-dimensional effects are examined, in the context of use of a solenoid for focusing and acceleration enhancement.
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title: An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB
format: conference proceeding
conference: AAC 2004 11th
year: 2004
7 authors: J.B. Rosenzweig | S. Hoover | M. Hogan | P. Muggli | M.C. Thompson | G. Travish | R. B. Yoder
abstract: The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, ) at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cerenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields.
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title: Status Report on SPARC Project
format: conference proceeding
conference: FEL 2004 26th
year: 2004
96 authors: A. Renieri | M. Carpanese | F. Ciocci | G. Dattoli | A. Di Pace | A. Doria | F. Flora | G. P. Gallerano | L. Giannessi | E. Giovenale | G. Messina | L. Mezi | P. L. Ottaviani | S. Pagnutti | G. Parisi | L. Picardi | M. Quattromini | G. Ronci | C. Ronsivalle | E. Sabia | M. Sassi | A. Zucchini | D. Alesini | M. Bellaveglia | S. Bertolucci | M.E. Biagini | C. Biscari | R. Boni | M. Boscolo | M. Castellano | A. Clozza | G. Di Pirro | A. Drago | A. Esposito | M. Ferrario | D. Filippetto | V. Fusco | A. Gallo | A. Ghigo | S. Guiducci | M. Incurvati | C. Ligi | F. Marcellini | M. Migliorati | C. Milardi | L. Palumbo | L. Pellegrino | M. Preger | P. Raimondi | R. Ricci | C. Sanelli | M. Serio | F. Sgamma | B. Spataro | A. Stecchi | A. Stella | F. Tazzioli | C. Vaccarezza | M. Vescovi | C. Vicario | M. Zobov | F. Alessandria | A. Bacci | I. Boscolo | F. Broggi | S. Cialdi | C. De Martinis | D. Giove | C. Maroli | V. Petrillo | M. Romè | L. Serafini | D. Levi | M. Mattioli | G. Medici | P. Musumeci | L. Catani | E. Chiadroni | S. Tazzari | C.J. Bocchetta | M. Danailov | G. D'Auria | M. Ferianis | A. Cianchi | A. D'Angelo | R. Di Salvo | A. Fantini | D. Moricciani | C. Schaerf | S. Reiche | J.B. Rosenzweig | G. Travish | D.H. Dowell | P. Emma | C. Limborg | D. Palmer
abstract: We review the status of FEL source activity of the ongoing SPARC FEL experiment, developed within the framework of a collaboration among ENEA, CNR, INFN, INFM, Sincrotrone Trieste and University of Rome Tor Vergata. The project is aimed at realising a SASE-FEL source, operating in the visible (around 500 nm), with an extended range of tunability down to the VUV (100 nm) by the use of the mechanism of non-linear harmonic generation. The development of the relevant activities foresees the realisation of an advanced 150 MeV photo- injector source, aimed at producing a high brightness electron beams, needed to drive a SASE-FEL experiment, and a 14 m long undulator. We present the status of the design and construction of SPARC FEL device. In particular we discuss the choice of the project parameters, their optimisation and the sensitivity of the SPARC performance to any parameter variation. We will show, using start-to-end simulations, what is the impact of the e- beam and of the undulator parameters on the characteristics of the output laser field and in particular on the amount of the non-linearly generated power at higher harmonics.
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title: VISA IB: Ultra-High Bandwidth, High Gain SASE FEL
format: conference proceeding
conference: FEL 2004 26th
year: 2004
15 authors: G. Andonian | A. Murokh | R. Agustsson | C. Pellegrini | S. Reiche | J.B. Rosenzweig | G. Travish | M. Babzien | I. Ben-Zvi | J. Y. Huang | V. Litvinenko | V. Yakimenko | M. Ferrario | L. Palumbo | C. Vicario
abstract: We report the results of a high energy spread SASE FEL experiment, the intermediary experiment linking the VISA I and VISA II projects. A highly chirped beam (1.7 %) was transported, without corrections of longitudinal aberrations in the ATF dogleg, and injected into the VISA undulator. The ouput radiation displayed an uncharacteristicly large bandwidth (12 %) with extremely stable lasing and mea- sured energy of about 2 ?J . Start-to-end simulations re- produced key features of the experiment and provided an insight into the michanisms giving rise to such a high band- width. These analyses have important implications on the VISA II experiment.
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title: UCLA Neptune Ramped Electron Bunch Experiment
format: journal article
publisher: AIP Conference Proceedings
year: 2004
5 authors: R. J. England | D. Alesini | A. Doyuran | P. Musumeci | J.B. Rosenzweig
abstract: A ramped electron bunch (i.e. one having a current density which rises linearly from the head to the tail and then drops sharply to zero) has been predicted to be an ideal drive beam for the plasma wake field accelerator due to the large transformer ratio it is capable of generating. A scheme was recently proposed for the creation of a relativistic electron bunch that approximates a ramped current profile [England, et al., AIP Conf. Proc. 647, p.884 (2002)], using a dogleg or dispersionless translating section as a bunch compressor. An experiment is underway at the Neptune laboratory using this scheme to create such a beam. The diagnostic being developed for measuring the temporal profile of the beam is an X-Band transverse deflecting mode cavity. 2004 American Institute of Physics
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title: Study of X-ray Harmonics of the Polarized Inverse Compton Scattering Experiment at UCLA
format: journal article
publisher: AIP Conference Proceedings
year: 2004
8 authors: A. Doyuran | J. England | C. Joshi | P. Musumeci | J.B. Rosenzweig | S. Tochitsky | G. Travish | O. Williams
abstract: We propose an Inverse Compton Scattering (ICS) experiment, which will investigate nonlinear properties of the scattering utilizing the terawatt CO2 laser system with various polarizations in Neptune Laboratory at UCLA. When the normalized amplitude of the vector potential a0 is larger than unity the scattering occurs in the nonlinear region; therefore, higher harmonics are also produced. We present a calculation tool for the Double Differential Spectrum (DDS) distribution and total number of photons produced for both head-on and 90 scattering. We decided to do the experiment at 90 to avoid complications due to strong diffraction of the incoming laser. We discuss the electron and laser beam parameters for the experiment. 2004 American Institute of Physics
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title: Study of a THz IFEL prebuncher for laser-plasma accelerators
format: journal article
publisher: AIP Conference Proceedings
year: 2004
7 authors: C. Sung | S. Ya. Tochitsky | P. Musumeci | J. Ralph | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: For monoenergetic acceleration of electrons, the injected particles need to be bunched with the same periodicity as the accelerating structure. In a laser-driven plasma beatwave accelerator, the accelerating structure (plasma wave) is phase-locked to the CO2 beat-wave used to drive it. Using the same beat-wave to generate high power FIR radiation via difference frequency mixing in GaAs ensures that the radiation has the same phase relationship as the plasma wave before it saturates and detunes from the pump. Therefore, this radiation can be used to prebunch an existing electron beam based on an Inverse Free Electron Laser (IFEL) concept. Here we report the progress on the proposed THz microbunching experiment in the Neptune laboratory. A 50 cm long prebuncher is optimized using simulation codes for minimum FIR power required. The injected 5ps long electron beam is expected to form a series of 45 m long microbunches containing over 40% of the injected current after 1.6 m drift space following the undulator. Preliminary experimental results on THz generation are also presented.
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title: Acceleration of electrons in a diffraction-dominated IFEL
format: journal article
publisher: FEL
year: 2004
16 authors: P. Musumeci | S. Ya. Tochitsky | S. Boucher | A. Doyuran | R. J. England | C. Joshi | C. Pellegrini | J. Ralph | J.B. Rosenzweig | C. Sung | S. Tolmachev | G. Travish | A. A. Varfolomeev | A. Varfolomeev Jr. | T. Yarovoi | R. Yoder.
abstract: We report on the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator ex- periment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in a 50 cm long undulator strongly tapered both in period and field amplitude. A CO2 10.6 ?m laser with power > 300 GW is used as the IFEL driver. The Rayleigh range of the laser ( ? 1.8 cm) is shorter than the undulator length so that the interaction is diffraction dom- inated. Few per cent of the injected particles are trapped in stable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometer. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. An energy gradient of > 70 MeV is inferred. In the second section of the undulator higher harmonic IFEL interaction is observed.
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title: Experimental characterization of an ultrafast Thomson scattering x-ray source with three-dimensional time and frequency-domain analysis
format: journal article
publisher:
year: 2004
18 authors: W. J. Brown | S. G. Anderson | C. P. J. Barty | S. M. Betts | R. Booth | J. K. Crane | R. R. Cross | D. N. Fittinghoff | D. J. Gibson | F. V. Hartemann | E. P. Hartouni | J. Kuba | G.P. Le Sage | D. R. Slaughter | A. M. Tremaine | A. J. Wootton | P. T. Springer | J.B. Rosenzweig
abstract: We present a detailed comparison of the measured characteristics of Thomson backscattered xrays produced at the Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures facility at Lawrence Livermore National Laboratory to predicted results from a newly developed, fully three-dimensional time and frequency-domain code. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, perpendicular wave vector components in the laser focus, and the transverse and longitudinal phase spaces of the electron beam are included. Electron beam energy, energy spread, and transverse phase space measurements of the electron beam at the interaction point are presented, and the corresponding predicted x-ray characteristics are determined. In addition, time-integrated measurements of the xrays produced from the interaction are presented and shown to agree well with the simulations.
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title: COMMISSIONING OF STRONG TAPERED UNDULATOR DEVELOPED
format: journal article
publisher:
year: 2004
7 authors: S.V. Tolmachev | A. A. Varfolomeev | A. Varfolomeev Jr. | T.V. Yarovoi | P. Musumeci | C. Pellegrini | J.B. Rosenzweig
abstract: Here we describe the manufactured KIAE-2p planar undulator designed for the Inverse Free Electron Laser experiment at the University of California in Los Angeles. New technology enabled to fabricate the installation responding to the stringent requirements on mechanical construction accuracy and magnetic field strong tapering. Results of the magnetic field measurements by different methods are given. The obtained magnetic field maps were used for final simulations of the acceleration process. It is shown that for nominal electron beam and laser beam parameters up to 30% of electrons can be captured and accelerated from initial 14 MeV up to 52 MeV. Special analysis of the undulator acceptances for these parameters is made. It is shown that the acceleration is possible up to energies >30 MeV for rather wide ranges of laser pulse energy, Rayleigh length and e.b. emittance.
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title: The SPARX project: R & D Activity towards X-Ray Sources
format: journal article
publisher:
year: 2004
80 authors: D.Alesini | S.Bertolucci | M. Bellaveglia | M.E.Biagini | R.Boni | M.Boscolo | M.Castellano | A.Clozza | G.Di Pirro | A.Drago | A.Esposito | M.Ferrario | D. Filippetto | V.Fusco | A.Gallo | A.Ghigo | S.Guiducci | M.Incurvati | C.Ligi | F.Marcellini | M.Migliorati | A.Mostacci | L.Palumbo | L.Pellegrino | M.Preger | P. Raimondi | R.Ricci | C.Sanelli | M.Serio | F.Sgamma | B.Spataro | A.Stecchi | A.Stella | F.Tazzioli | C.Vaccarezza | M.Vescovi | C.Vicario | F.Alessandria | A.Bacci | I.Boscolo | F.Broggi | S.Cialdi | C.De Martinis | D.Giove | C.Maroli | M. Mauri | V.Petrillo | M. Romè | L.Serafini | M.Mattioli | P. Musumeci | L.Catani | E.Chiadroni | A. Cianchi | C. Schaerf | F.Ciocci | G.Dattoli | A. Di Pace | A.Doria | F.Flora | G.P.Gallerano | L.Giannessi | E.Giovenale | G.Messina | L.Mezi | P.L.Ottaviani | S. Pagnutti | G. Parisi | L.Picardi | M.Quattromini | A.Renieri | C.Ronsivalle | A. Torre | A. Zucchini | S. De Silvestri | M. Nisoli | S. Stagira | J.B. Rosenzweig | S. Reiche | P.Emma
abstract: SPARX is an evolutionary project proposed by a collaboration among ENEA-INFN-CNR-Universita` di Roma Tor Vergata aiming at the construction of a FEL- SASE X-ray source in the Tor Vergata Campus. The first phase of the SPARX project, funded by Government Agencies, will be focused on R&D activity on critical components and techniques for future X-ray facilities as described in this paper.
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title: Plasma density transition trapping as a possible high-brightness electron beam source
format: journal article
publisher: Physical Review Special Topics- Accelerators and Beams
year: 6 January 2004
3 authors: M.C. Thompson | J.B. Rosenzweig | Suk, H.
abstract: Plasma density transition trapping is a recently proposed self-injection scheme for plasma wakefield accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wakefield. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional particle-in-cell simulations show that these parameters can be optimized by manipulating the plasma density profile.We also develop, and support with simulations, a set of scaling laws that predicts how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness ? 5 10^14 A/(mrad)^2. A proof-of-principle transition trapping experiment is planned for the near future. The proposed experiment is described in detail.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Simulations, Scaling, and Accelerating Wakefields
format: preprint
year: 2004
4 authors: J.B. Rosenzweig | N. Barov | M.C. Thompson | R. B. Yoder
abstract: The energy loss and gain of a beam in the nonlinear, ��blowout�� regime of the plasma wakefield accelerator, which features ultrahigh accelerating fields, linear transverse focusing forces, and nonlinear plasma motion, has been asserted, through previous observations in simulations, to scale linearly with beam charge. Additionally, from a recent analysis by Barov et al., it has been concluded that for an infinitesimally short beam, the energy loss is indeed predicted to scale linearly with beam charge for arbitrarily large beam charge. This scaling is predicted to hold despite the onset of a relativistic, nonlinear response by the plasma, when the number of beam particles occupying a cubic plasma skin depth exceeds that of plasma electrons within the same volume. This paper is intended to explore the deviations from linear energy loss using 2D particle-in-cell simulations that arise in the case of experimentally relevant finite length beams. The peak accelerating field in the plasma wave excited behind the finite-length beam is also examined, with the artifact of wave spiking adding to the apparent persistence of linear scaling of the peak field amplitude into the nonlinear regime. At large enough normalized charge, the linear scaling of both decelerating and accelerating fields collapses, with serious consequences for plasma wave excitation efficiency. Using the results of parametric particle-in-cell studies, the implications of these results for observing severe deviations from linear scaling in present and planned experiments are discussed.
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title: Non-Resonant Beat-Wave Excitation of Constant Phase-Velocity, Relativistic Plasma Waves for Charged-Particle Acceleration
format: journal article
publisher:
year: 2004
10 authors: C. V. Filip | R. Narang | S. Ya. Tochitsky | C. E. Clayton | P. Musumeci | R. B. Yoder | K. A. Marsh | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: The nonresonant beat-wave excitation of relativistic plasma waves is studied in two-dimensional simulations and experiments. It is shown through simulations that, as opposed to the resonant case, the accelerating electric fields associated with the nonresonant plasmons are always in phase with the beat-pattern of the laser pulse. The excitation of such nonresonant relativistic plasma waves is shown to be possible for plasma densities as high as 14 times the resonant density. The density fluctuations and the fields associated with these waves have significant magnitudes, facts confirmed experimentally using collinear Thomson scattering and electron injection, respectively. The applicability of these results towards eventual phase-locked acceleration of prebunched and externally injected electrons is discussed.
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title: Experiments on laser driven beatwave acceleration in a ponderomotively formed plasma channel
format: journal article
publisher: Physics of Plasmas
year: 2004
10 authors: S. Ya. Tochitsky | R. Narang | C. V. Filip | P. Musumeci | C. E. Clayton | R. B. Yoder | K. A. Marsh | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: A 10 ps long beam of 12 MeV electrons is externally injected into a ~3-cm long plasma beatwave excited in a laser ionized hydrogen gas. The electrons have been accelerated to 50 MeV with a gradient of ~1.3 GeV/m. It is shown that when the effective plasma wave amplitude-length product is limited by ionization-induced defocusing (IID), acceleration of electrons is significantly enhanced by using a laser pulse with a duration longer than the time required for ions to move across the laser spot size. Both experiments and two-dimensional simulations reveal that, in this case, self-guiding of the laser pulse in a ponderomotively formed plasma channel occurs. This compensates for IID and drives the beatwave over the longer length compared to when such a channel is not present.
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title: Beam Shaping and Compression Scheme for the UCLA Neptune Laboratory
format: conference proceeding
conference: PAC 2003
year: 2003
4 authors: R. J. England | P. Musumeci | R. Yoder | J.B. Rosenzweig
abstract: We have recently added a dispersionless translating section to the UCLA Neptune linear accelerator beamline. This new section of beamline will serve as a venue for beam shaping and compression experiments using the 14MeV electron beam produced by the UCLA Neptune PWT linac and newly installed photoinjector. An examination of the first and second-order optics indicates that when certain nonlinear effects are minimized through the use of sextupole magnets, the longitudinal dispersion is dominated by a negative R56 which, for an appropriately chirped initial beam, can be used to create a ramped beam of a few picosecond duration that would be ideal for driving large amplitude wake fields in a plasma and producing high transformer ratios. The beamline is now in operation. Preliminary data indicate that the beamline optics are well-predicted by simulation and that sextupoles can be used successfully to eliminate nonlinear horizontal dispersion. Future experiments are planned for measuring beam compression (using CTR autocorrelation) and doing longitudinal phase space tomography (using a transverse deflecting cavity).
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title: Design and Operation of Pegasus Thermionic Cathode
format: conference proceeding
conference: PAC 2003
year: 2003
6 authors: P. Frigola | G. Andonian | Sven Reiche | J.B. Rosenzweig | S. Telfer | G. Travish
abstract: A new thermionic cathode has been developed and installed for use on The PEGASUS plane wave transformer injector. The novel design of the LaB6 cathode allows for thermionic emission as well as photoinjector operation. Test stand measurements as well as in situ operational experience are reported.
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title: The FEL Program at the PEGASUS Injector
format: conference proceeding
conference: PAC 2003
year: 2003
6 authors: Sven Reiche | G. Andonian | P. Frigola | J.B. Rosenzweig | S. Telfer | and G. Travish
abstract: The PEGASUS photo injector at UCLA can produce a photo electrons beam with a normalized emittance of 2 mm mrad at an energy of 12-15 MeV, capable of driving a Free-Electron Laser in the mid IR regime. The FEL program, associated with the PEGASUS injector and presented here, is based on a Self-Amplifying Spontaneous Emission (SASE) FEL. The studies focus on increasing the efficiency of an FEL by novel undulator design and compensation of diffraction effects, using waveguides of millimeter size. In this presentation we also discuss the possibility of the PEGASUS FEL as a THz user facility.
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title: Status of the UCLA PEGASUS Laboratory
format: conference proceeding
conference: PAC 2003
year: 2003
6 authors: G. Andonian | P. Frigola | Sven Reiche | J.B. Rosenzweig | S. Telfer | G. Travish
abstract: The PEGASUS laboratory is a versatile radiation facility dedicated to the advancement of novel concepts in beam physics. The installation of a new LaB$_6$ cathode will allow for both thermionic emission and photoinjection operation. The PEGASUS plane wave transformer injector has been conditioned to 20 MW of RF power. Recent operations show a 15 MeV dark current beam that will be used for beam radiation studies. An upgrade to the drive laser system has been explored and will be realized shortly. This paper will describe and report the status of the various subsystems of the PEGASUS laboratory and outline the experiments underway, such as innovative beam instrumentation, surface effects in optical transition radiation, Thomson scattering, and waveguide SASE FEL.
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title: A Slab-Symmetric Dielectric-Loaded Structure for High-Gradient Acceleration at THz
format: conference proceeding
conference: PAC 2003
year: 2003
2 authors: R. B. Yoder | J.B. Rosenzweig
abstract: We present a design for a slab-symmetric accelerating structure to be resonantly excited at terahertz frequencies. The device, consisting of a vacuum gap between dielectric-lined walls, combines the advantages of a slab geometry (including strong suppression of transverse beam wakefields and low power density) with the existence of a resonant mode having phase synchronism with relativistic electrons. Accelerating fields of hundreds of MeV/m are predicted when the structure is powered by a high-power FIR radiation source in development at UCLA. Simulation of the structure fields is described and compared with theory, and an experimental program is discussed.
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title: Energy Loss and Accelerating Field in the Plasma Wakefield Accelerator
format: preprint
year: 2003
4 authors: J.B. Rosenzweig | R. B. Yoder | N. Barov | M.C. Thompson
abstract:
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title: The UCLA/NICADD Plasma Density Transition Trapping Experiment
format: conference proceeding
conference: PAC 2003
year: 2003
6 authors: M.C. Thompson | W. Lu | W. Mori | J.B. Rosenzweig | G. Travish | N. Barov
abstract: Plasma density transition trapping is a recently purposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. Two and three dimensional Particle-In-Cell (PIC) simulations show that electron beams of substantial charge can be captured using this technique, and that the beam parameters such as emittance, energy spread, and brightness can be optimized by manipulating the plasma density profile. These simulations also predict that transition trapping can produce beams with brightness > 5x10^14 Amp/(m-rad)^2 when scaled to high plasma density regimes. A proof-of-principle plasma density transition trapping experiment is planned for the near future. This experiment is a collaboration between UCLA and the Northern Illinois University (NICADD). The goal of experiment is to capture a ~100 pC beam with ~4% rms energy spread out of a 2 x 10^13 cm^-3 peak density plasma using a ~6nC, 14 MeV drive beam. Status and progress on the experiment are reported.
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title: Comparison of the coherent radiation-induced microbunching instability in a free-electron laser and a magnetic chicane
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2003
2 authors: Sven Reiche | J.B. Rosenzweig
abstract: A self-amplified spontaneous emission free-electron laser (SASE FEL) is a device which is based on the creation of a very intense, relativistic electron beam which has very little temperature in all three phase planes. The beam in this system is described as having "high brightness,'' and when it is bent repetitively in a magnetic undulator, undergoes a radiation-mediated microbunching instability. This instability can amplify the original radiation amplitude at a particular, resonant wavelength by many orders of magnitude. In order to obtain high brightness beams, it is necessary to compress them to obtain higher currents than available from the electron source. Compression is accomplished by the use of magnetic chicanes, which are quite similar to, if much longer than, a single period of the undulator. It should not be surprising that such chicanes also support a radiation-mediated microbunching interaction, which has recently been investigated, and has been termed coherent synchrotron radiation (CSR) instability. The purpose of this paper is to compare and contrast the characteristics of the closely related FEL and CSR microbunching instabilities. We show that a high-gain regime of the CSR instability exists which is formally similar to the FEL instability.
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title: A Fast Method to Estimate the Gain of the Microbunch Instability in a Bunch Compressor
format: conference proceeding
conference: PAC 2003
year: 2003
2 authors: Sven Reiche | J.B. Rosenzweig
abstract: For the users of the high-brightness radiation sources of free-electron lasers it is necessary to reduce the FEL pulse length to 10 fs and below for time-resolving pump and probe experiments. Although it can be achieved by conventional compression methods for the electron beam or the chirped FEL pulse, the technical realization is demanding. In this presentation we study the impact of undulator wakefields and how their properties can be used to reduced the amplifying part of the bunch to the desired length. Methods of actively controlling the wakefields are presented.
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title: Status of the Inverse Free Electron Laser Experiment at the Neptune Laboratory
format: conference proceeding
conference: PAC 2003
year: 2003
10 authors: P. Musumeci | C. Pellegrini | J.B. Rosenzweig | S. Tochitsky | G. Travish | R. Yoder | A. A. Varfolomeev | Tolmachev, S. | A. Varfolomeev Jr. | T. Yarovoi
abstract: We report on the status of the Inverse Free Electron Laser accelerator experiment under construction at the UCLA Neptune Laboratory. This experiment will use a 400 GW CO2 laser to accelerate through a tapered undulator an electron beam from 14.5 MeV up to 55 MeV. The scheme proposed is the diffraction dominated IFEL interaction where the Rayleigh range of the laser beam is 3.5 cm, much shorter than the interaction length (the undulator length is 50 cm). The undulator is strongly tapered in both field and period. The present status of the experiment is reported.
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title: A Plasma-Assisted High-Brightness X-Ray Source via Inverse Compton Scattering
format: preprint
year: 2003
3 authors: J.B. Rosenzweig | R. B. Yoder | G. Travish
abstract:
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title: An Adjustable Permanent Magnet Quadrupole Final Focus System for Low Energy Experiments
format: conference proceeding
conference: PAC 2003
year: 2003
7 authors: J. Lim | P. Frigola | J.B. Rosenzweig | S. Telfer | G. Travish | W. Brown | A. Tremaine
abstract: The final focus system for the Thomson X-ray scattering experiment termed PLEIADES (Picosecond Laser-Electron InterAction for Dynamic Evaluation of Structures) at LLNL demands ultra-high field gradient quadrupoles in order to focus initially small beams to 10-20 micron spot sizes. This scheme circumvents limitations due to chromatic aberrations and space-charge effects in this relatively low energy (<100 Mev) system. The final focus scheme is based on an ultra-high gradient (300T/m) quadrupole which employs the Halbach 16-piece, permanent magnet design. Use of this optimized goemetry, NdFeB material, and a small (4 mm) bore allows the desired field gradient, and few cm focal length, to be achieved. The adjustability of the focusing system is obtained by changing the relative longitudinal positions of sub-component focusing and defocusing magnets on precision movers. We present the results of RADIA 3D design simulations, and measurement of prototype magnets. We also discuss the results of beam dynamics simulations of the PLEIADES system using both envelope and tracking codes.
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title: Pulse Compression via Velocity Bunching with the LLNL Thomson X-Ray Source Photoinjector
format: conference proceeding
conference: PAC 2003
year: 2003
5 authors: S. Anderson | W. J. Brown | A.M. Tremaine | P. Musumeci | J.B. Rosenzweig
abstract: We report the compression of a high brightness, relativistic electron beam to rms lengths below 300 femtoseconds using the velocity compression technique in the LLNL Thomson X-ray source photoinjector. The results are consistent with analytical and computational models of this process. The emittance evolution of the beam during compression is investigated in simulation and found to be controllable with solenoid focusing.
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title: Design and Status of the VISA II Experiment
format: conference proceeding
conference: PAC 2003
year: 2003
12 authors: G.Andonian | R.Agustsson | A. Murokh | C.Pellegrini | Sven Reiche | J.B. Rosenzweig | G. Travish | M. BABZIEN | I. Ben-Zvi | V. Yakimenko | L. Palumbo | C. VICARIO
abstract: VISA II is the follow-up project to the successful Visible to Infrared SASE Amplifier (VISA) experiment at the Accelerator Test Facility (ATF) in Brookhaven National Lab (BNL). This paper will report the motivation for and status of the two main experiments associated with the VISA II program. One goal of VISA II is to perform an experimental study of the physics of a chirped beam SASE FEL at the upgraded facilities of the ATF. This requires a linearization of the transport line to preserve energy chirping of the electron beam at injection. The other planned project is a strong bunch compression experiment, where the electron bunch is compressed in the chicane, and the dispersive beamline transport, allowing studies of deep saturation.
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title: Properties of the ultrashort gain length, self-amplified spontaneous emission free-electron laser in the linear regime and saturation
format: journal article
publisher: Physical Review E
year: 2003
26 authors: A. Murokh | R. Agustsson | M. Babzien | I. Ben-Zvi | L. Bertolini | K. van Bibber | R. Carr | M. Cornacchia | P. Frigola | J. Hill | E. Johnson | L. Klaisner | G.P. Le Sage | M. Libkind | R. Malone | H-D. Nuhn | C. Pellegrini | Sven Reiche | G. Rakowsky | J.B. Rosenzweig | Ruland, R. | Skaritka, J. | A. Toor | A. Tremaine | X. Wang | V. Yakimenko
abstract: VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission (SASE) free-electron laser (FEL), which achieved saturation at 840 nm within a single-pass 4-m undulator. The experiment was performed at the Accelerator Test Facility at BNL, using a high brightness 70-MeV electron beam. A gain length shorter than 18 cm has been obtained, yielding a total gain of 2x10(8) at saturation. The FEL performance, including the spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. Results are compared to the three-dimensional SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL systems. An agreement between simulations and experimental results has been obtained at an unprecedented level of detail.
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title: Horizontal Phase-Space Distortions Arising from Magnetic Pulse Compression of an Intense, Relativistic Electron Beam
format: journal article
publisher: Physical Review Letters
year: 2003
4 authors: S. Anderson | J.B. Rosenzweig | P. Musumeci | M.C. Thompson
abstract: We report detailed measurements of the transverse phase space distortions induced by magnetic chicane compression of a high brightness, relativistic electron beam to subpicosecond length. A strong bifurcation in the phase space is observed when the beam is strongly compressed. This effect is analyzed using several computational models and is correlated to the folding of longitudinal phase space. The impact of these results on current research in collective beam effects in bending systems and implications for future short wavelength free-electron lasers and linear colliders are discussed.
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title: Acceleration of Injected Electrons In A Laser Beatwave Experiment
format: conference proceeding
conference: PAC 2003
year: 2003
10 authors: S. Ya. Tochitsky | R. Narang1 | C.V. Filip1 | P. Musumeci | C.E. Clayton | R. Yoder | K.A. Marsh1 | J.B. Rosenzweig | C. Pellegrini | and C. Joshi11
abstract: Plasma-based accelerators of particles are of great interest because plasmas can sustain very strong electric fields. They are utilizing a relativistic plasma wave with a phase velocity close to the speed of light driven by a high-power laser beam. The Neptune Laboratory at UCLA is being used for plasma beatwave acceleration of injected electrons. Here, a two-wavelength laser pulse (frequencies w1,w2) resonantly drives a longitudinal electron plasma wave of frequency equal to w1-w2, providing a field strength of GeV/m and, therefore, accelerates an injected electron beam at this very high gradient. A 10 ps beam of 12 MeV electrons is loaded in a 3-cm long plasma beatwave accelerator driven by a TW CO2 laser pulse. At the resonance condition, the electrons have been accelerated to 50 MeV with a gradient of ~1.3 GeV/m. It is shown that for large volume diffraction limited plasmas, when efficiency of the plasma wave excitation is restricted by ionization-induced refraction, acceleration of electrons is enhanced significantly by using asymmetric (fast front and slow fall) long pulses. 2D PIC simulations revealed that guiding of the laser pulse in a ponderomotive, self-induced ion channel, formed ~200 ps after the field ionization, allows compensation for the ionization-induced defocusing and efficient driving of the beatwave over the entire length.
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title: The ORION Facility
format: conference proceeding
conference: PAC 2003
year: 2003
10 authors: R.J. Noble | E.R. Colby | D. T. Palmer | R.H. Siemann | D. Walz | R. Byer | C. Joshi | W. Mori | J.B. Rosenzweig | T. Katsouleas
abstract: ORION will be a user-oriented research facility for understanding the physics and developing the technology for future high-energy particle accelerators. The ORION Facility will bring together the needed resources for performing a wide range of experiments in advanced accelerator and beam physics. The facility has as its centerpiece the Next Linear Collider Test Accelerator (NLCTA) within End Station B at the SLAC Central Research Yard. That site will be modified with the addition of a new high-brightness photoinjector, its associated drive laser and rf power system, a user laser room, a low-energy experimental hall supplied with electron beams up to approximately 60 MeV in energy, and a high-energy hall supplied with beams up to 350 MeV. Facility construction is anticipated to start in October 2003, contingent upon funding approval, and first beam is planned for 2005. The first experiment at ORION, the laser acceleration experiment E163, has been approved by SLAC. In this paper, results are presented on the revised facility layout and design which came out of the 2nd ORION Workshop in February 2003, and the beam physics design of the injector and the beamlines for the low and high-energy experimental halls.
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title: Start to End Simulations for the SPARX Proposal
format: conference proceeding
conference: PAC 2003
year: 2003
18 authors: M. Biagini | M. Boscolo | M. Ferrario | V. Fusco | S. Guiducci | B. Spataro | C. Vaccarezza | M. Zobov | L. Serafini | R. Bartolini | G. Dattoli | L. Giannessi | L. Mezi | M. Quattromini | C. Ronsivalle | E. Chiadroni | P. Emma | J.B. Rosenzweig
abstract: The resource allocation in the Italian National Research Plan (PNR) for the development of a coherent ultra-brilliant X-ray source, based on a SASE Free Electron Laser, brought about the formation of a CNR-ENEA-INFN- University of Roma "Tor Vergata" study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated leading to the SPARX proposal. We report in this paper the results of start to end simulations concerning the option based on an S-band normal conducting linac. Saturation at 1-10 nm can be achieved in a 40 m long undulator provided the peak current delivered by the linac is 2.5 kA at 2.5 GeV with rms normalized slice emittance of the order of 1 _m and the energy spread less than 0.1%. One of the most critical systems is the bunch compressor. The effects on beam dynamics of a magnetic chicane system and a rectilinear RF compressor (based on velocity bunching), integrated in a high brightness photoinjector, are analyzed and compared in this paper.
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title: The SPARC Project: A High Brightness Electron Beam Source at LNF to Drive a SASE-FEL Experiment
format: conference proceeding
conference: PAC 2003
year: 2003
75 authors: D. Alesini | S. Bertolucci | M. Biagini | C. Biscari | R. Boni | M. Boscolo | M. Castellano | A. Clozza | G. Di Pirro | A. Drago | A. Esposito | M. Ferrario | V. Fusco | A. Gallo | A. Ghigo | S. Guiducci | M. Incurvati | C. Ligi | F. Marcellini | M. Migliorati | C. Milardi | L. Palumbo | L. Pellegrino | M. Preger | P. Raimondi | R. Ricci | C. Sanelli | M. Serio | F. Sgamma | B. Spataro | A. Stecchi | A. Stella | F. Tazzioli | C. Vaccarezza | M. Vescovi | C. Vicario | M. Zobov | F. Alessandria | A. Bacci | I. Boscolo | F. Broggi | S. Cialdi | C. DeMartinis | D. Giove | C. Maroli | V. Petrillo | M. Rome | L. Serafini | D. Levi | M. Mattioli | L. Catani | E. Chiadroni | S. Tazzari | R. Bartolini | F. Ciocci | G. Dattoli | A. Doria | F. Flora | G. P. Gallerano | L. Giannessi | E. Giovenale | G. Messina | L. Mezi | P. L. Ottaviani | L. Picardi | M. Quattromini | A. Renieri | C. Ronsivalle | A. Cianchi | A. D'Angelo | R. Di Salvo | A. Fantini | D. Moricciani | C. Schaerf | J.B. Rosenzweig
abstract: The Project SPARC (Sorgente Pulsata e Amplificata di Radiazione Coerente), proposed by a collaboration among ENEA-INFN-CNR-Universita' di Roma "Tor Vergata" -INFM-ST, was recently approved by the Italian Government and will be built at LNF of INFN. The aim of the project is to promote an R&D activity oriented to the development of a coherent ultra-brilliant X-ray source in Italy. This collaboration has identified a program founded on two main issues: the generation of ultra-high peak brightness electron beams and of resonant higher harmonics in the SASE-FEL process.
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title: The UCLA Pegasus Plane-Wave Transformer Photoinjector
format: conference proceeding
conference: PAC 2003
year: 2003
6 authors: G. Travish | G. Andonian | P. Frigola | Sven Reiche | J.B. Rosenzweig | and S. Telfer
abstract: A photoinjector based on a multicell plane wave transformer accelerating structure has been commissioned at the UCLA Department of Physics' Pegasus Laboratory. Design and construction of the novel structure have been previously reported [J. Rosenzweig, et al. PAC Proceedings 1997], and recent operation with a thermionic cathode is being presented at this conference [P. Frigola, et al. these proceedings]. This paper describes the planned operation of the PWT gun as a photoinjector, including design and construction details of the drive laser. Progress to date and future plans are discussed.
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title: Generation of High Brightness X-Rays with the PLEIADES Thomson X-Ray Source
format: conference proceeding
conference: PAC 2003
year: 2003
14 authors: W. J. Brown | S. Anderson | C. P. J. Barty | J. K. Crane | R. R. Cross | D. N. Fittinghoff | F. V. Hartemann | J. Kuba | G.P. Le Sage | D. R. Slaughter | P. T. Springer | A. Tremaine | J.B. Rosenzweig | D. J. Gibson
abstract: The use of short laser pulses to generate high peak intensity, ultra-short x-ray pulses enables exciting new experimental capabilities, such as femtosecond pump-probe experiments used to temporally resolve material structural dynamics on atomic time scales. PLEIADES (Picosecond Laser Electron InterAction for the Dynamic Evaluation of Structures) is a next generation Thomson scattering x-ray source being developed at Lawrence Livermore National Laboratory (LLNL). Ultra-fast picosecond x-rays (10-200 keV) are generated by colliding an energetic electron beam (20-100 MeV) with a high intensity, sub-ps, 800 nm laser pulse. The peak brightness of the source is expected to exceed 1020 photons/s/0.1 bandwidth/mm2/mrad2. Simulations of the electron beam production, transport, and final focus are presented. Electron beam measurements, including emittance and final focus spot size are also presented and compared to simulation results. Measurements of x-ray production are also reported and compared to theoretical calculations.
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title: Velocity Bunching Experiment at the Neptune Laboratory
format: conference proceeding
conference: PAC 2003
year: 2003
3 authors: P. Musumeci | R. B. Yoder | J.B. Rosenzweig
abstract: In this paper we describe the rectilinear compression experiment at the Neptune photoinjector at UCLA. The electron bunches have been shortened to sub-ps pulse length by chirping the beam energy spectrum in a short S-band high gradient standing wave RF cavity and then letting the electrons undergo velocity compression in the following rectilinear drift. Using a standard Martin Puplett interferometer to characterize coherent transition radiation from the beam, we measured bunch lengths as short as 0.4 ps with compression ratio in excess of 10 for an electron beam of 7 MeV energy and charge up to 300 pC.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis
format: thesis
year: 2003
4 authors: N. Barov | J.B. Rosenzweig | M.C. Thompson | R. Yoder
abstract:
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title: The VISA FEL: an ultra-short gain length, saturated, self-amplified spontaneous emission free-electron laser
format: preprint
year: May 31, 2002
1 author: J.B. Rosenzweig
abstract:
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title: Monitoring and Manipulation of Sub-picosecond Beams
format: preprint
year: May 30, 2002
1 author: J.B. Rosenzweig
abstract: Outline: Applications of sub-picosecond beams: a UCLA-centric view Sub-picosecond beam generation Sub-picosecond beam manipulation Sub-picosecond beam diagnosis The future
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title: Velocity Bunching: ORION, PLEIADES and NEPTUNE
format: preprint
year: May 3, 2002
1 author: J.B. Rosenzweig
abstract:
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title: Accelerator and Charged Particle Beam Physics at UCLA
format: preprint
year: March 2002
1 author: J.B. Rosenzweig
abstract: Outline: What do we do? Who is involved What is current highlights of the research and education programs? Where are the future opportunities
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title: Experimental Experience in High Brightness Beams and SASE FELs at UCLA
format: preprint
year: June 6, 2002
1 author: J.B. Rosenzweig
abstract: Outline: Introduction to the UCLA Particle Beam Physics Laboratory (PBPL) High Brightness Beam Generation and Manipulation SASE FELs: Experimental Results Future work at UCLA
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title: Results of the VISA SASE FEL Experiment at 840 nm
format: conference proceeding
conference: FEL 2002 24th
year: 2003
26 authors: A. Murokh | R. Agustsson | M. BABZIEN | I. Ben-Zvi | L. Bertolini | K. van Bibber | R. Carr | M. Cornacchia | P. Frigola | J. Hill | E. Johnson | L. Klaisner | G.P. Le Sage | M. Libkind | R. Malone | H-D. Nuhn | C. Pellegrini | Sven Reiche | G. Rakowsky | J.B. Rosenzweig | Ruland, R. | Skaritka, J. | A. Toor | A. Tremaine | X. Wang | V. Yakimenko
abstract: VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission (SASE) free-electron laser (FEL), which achieved saturation at 840 nm within a single-pass 4-m undulator. A gain length shorter than 18 cm has been obtained, yielding the gain of 2x10(8) at saturation. The FEL performance, including the spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. The results are compared to 3-D SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL system. Detailed agreement between simulations and experimental results is obtained over the wide range of the electron beam parameters.
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title: A fast method to estimate the gain of the microbunch instability in a bunch compressor
format: conference proceeding
conference: FEL 2002 24th
year: 2003
2 authors: Sven Reiche | J.B. Rosenzweig
abstract: To reach high peak currents driving Free-Electron Lasers an initial chirped electron bunch is compressed in a bunch compressor. The interaction of the electron beam with its radiation field can yield a collective instability, which amplifies any initial modulation in the current profile. We present a model, which allows to derive an explicit analytical expression for the gain of the microbunch instability. The results are compared to those of the more complex analytical models.
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title: A Resonant, THz Slab-Symmetric Dielectric-Based Accelerator
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2003
2 authors: R. B. Yoder | J.B. Rosenzweig
abstract: Slab-symmetric dielectric-loaded structures, consisting of a vacuum gap between dielectric-lined conducting walls, have become a subject of interest for highgradient acceleration of high-charge beams due to their simplicity, relatively low power density, and advantageous beam dynamics. Such a structure can be resonantly excited by an external power source and is known to strongly suppress transverse wakefields. Motivated by the prospect of a high-power FIR radiation source, currently under construction at UCLA, we investigate a high-gradient slabsymmetric accelerator powered by up to 100 MW of laser power at 340 ?m, with a predicted gradient near 100 MeV/m. Theory and simulation studies of the structure fields and wakes are presented, with an outline of a future experiment.
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title: Status of the UCLA PEGASUS Injector Laboratory
format: conference proceeding
conference: FEL 2002 24th
year: 2003
6 authors: G. Andonian | P. Frigola | Sven Reiche | J.B. Rosenzweig | S. Telfer | and G. Travish
abstract: The PEGASUS plane wave transformer injector has been conditioned to 20 MW of RF power. Initial operations show a 15 MeV dark current beam that will be used for beam radiation studies. The design of a new LaB_6 cathode will allow for both thermionic emission and photoinjection operation. Experiments currently planned include novel beam instrumentation, surface effects in optical transition radiation, and waveguide SASE FEL.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2003
3 authors: N. Barov | J.B. Rosenzweig | M.C. Thompson
abstract: There has been much interest in the blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high fields and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams.
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title: Measurements of nonlinear harmonic radiation and harmonic microbunching in a visible SASE FEL
format: conference proceeding
conference: FEL 2002 24th
year: 2003
13 authors: A. Tremaine | X. J. Wang | M. Babzien | I. Ben-Zvi | M. Cornacchia | R. Malone | A. Murokh | H. D. Nuhn | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | Skaritka, J. | V. Yakimenko
abstract: The experimental characterization of nonlinear harmonic generation (NHG) and electron beam microbunching at saturation from a visible SASE FEL are presented in this report. The gain lengths, spectra and energies of NHG were experimentally measured up to the third harmonic, and agree with theoretical predictions. Electron beam microbunching in both the fundamental and the second harmonic as the function of the SASE output were experimentally observed over the full range of SASE gain. The bunching factors for both the fundamental (b(1)) and second harmonic (b(2)) were experimentally characterized at saturation. The microbunching data provides another test of SASE saturation as well as correlating the NHG and electron beam microbunching modes to the fundamental SASE.
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title: Velocity bunching experiment at the Neptune Laboratory
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2003
3 authors: P. Musumeci | R. Yoder | J.B. Rosenzweig
abstract: In this paper we describe the rectilinear compression ex- periment at the Neptune photoinjector at UCLA. The elec- tron bunches have been shortened to sub-ps pulse length by chirping the beam energy spectrum in a short S-band high gradient standing wave RF cavity and then letting the elec- trons undergo velocity compression in the following rec- tilinear drift. Using a standard Martin Puplett interferom- eter to characterize coherent transition radiation from the beam, we measured bunch lengths as short as 0.4 ps with compression ratio in excess of 10 for an electron beam of 7 MeV energy and charge up to 300 pC.
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title: Plasma Density Transition Trapping as a Possible High-Brightness Electron Beam Source
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2003
3 authors: M.C. Thompson | J.B. Rosenzweig | H. Suk
abstract: Plasma density transition trapping is a recently purposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electron in a plasma wake-field. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional Particle-In-Cell (PIC) simulations show that these parameters can be optimized by manipulating the plasma density profile. We also develop, and support with simu- lations, a set of scaling laws that predict how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness ≥ 5 x 10 14 Amp / (m- rad) 2 . A proof-of-principle transition trapping experiment is planned for the UCLA Neptune Laboratory in the near future. The proposed experiment and its status are described in detail.
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title: Plasma Density Transition Trapping as a Possible High-Brightness Electron Beam Source
format: conference proceeding
conference: AAC 2002 10th
year: 2002
2 authors: J.B. Rosenzweig | M.C. Thompson
abstract: Plasma density transition trapping is a recently proposed self-injection scheme for plasma wakefield accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wakefield. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional particle-in-cell simulations show that these parameters can be optimized by manipulating the plasma density profile.We also develop, and support with simulations, a set of scaling laws that predicts how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness 5 1014 A= mrad 2. A proof-ofprinciple transition trapping experiment is planned for the near future. The proposed experiment is described in detail.
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title: Bunched Beam Injection in a Plasma Accelerator
format: conference proceeding
conference: AAC 2002 10th
year: 2002
6 authors: S. Ya. Tochitsky | P. Musumeci | C. E. Clayton | C. Pellegrini | J.B. Rosenzweig | C. Joshi
abstract: An experiment on phase-locked injection of ~ 100 fs electron bunches in a plasma beat wave accelerator is presented. We consider using an IFEL microbunching technique to produce ultrashort electron bunches prebunched at the exact wavelength of the plasma wave 340 Jim (~lTHz). It is proposed to generate 100 MW of 1 THz radiation by difference frequency generation in a nonlinear crystal, mixing the same two CC>2 lines as used to drive the plasma accelerator.
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title: A Resonant, THz Slab-Symmetric Dielectric-Based Accelerator
format: conference proceeding
conference: AAC 2002 10th
year: 2002
2 authors: R. B. Yoder | J.B. Rosenzweig
abstract: Slab-symmetric dielectric-loaded structures, consisting of a vacuum gap between dielectric-lined conducting walls, have become a subject of interest for short-wavelength acceleration due to their simplicity, relatively low power density, and advantageous beam dynamics. Such a structure can be resonantly excited by an external power source and is known to strongly suppress transverse wakefields. Motivated by the prospect of a high-power FIR radiation source, currently under construction at UCLA, we investigate a high-gradient slab- symmetric accelerator powered by up to 100 MW of laser power at 340 um, with a predicted gradient near 100 MeV/m. Three-dimensional simulation studies of the structure fields and wakes are presented and compared with theory, and a future experiment is discussed.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Nonlinear plasma response and linear scaling
format: conference proceeding
conference: AAC 2002 10th
year: 2002
4 authors: J.B. Rosenzweig | N. Barov | M.C. Thompson | R.B. Yoder
abstract: There has been much experimental and theoretical interest in blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high accelerating fields, linear transverse focusing forces, and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity, and relativistic plasma effects become important or dominant. The physical bases for this persistence of linear response are pointed out. As a byproduct of our analysis, we re-examine the issue of field divergence as the point-charge limit is approached, suggesting an important modification of commonly held views of evading unphysical energy loss. Deviations from linear behavior are investigated using simulations with finite length beams. The peak accelerating field in the plasma wave excited behind a finite-length beam is also examined, with the artifact of wave spiking adding to the apparent persistence of linear scaling of the peak field amplitude well into the nonlinear regime. On the other hand, at large enough normalized charge, linear scaling of fields collapses, with serious consequences for plasma wave excitation efficiency. The dramatic implications of these results for observing the collapse of linear scaling in planned experiments are discussed.
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title: Longitudinal Beam Shaping and Compression Scheme for the UCLA Neptune Laboratory
format: conference proceeding
conference: AAC 2002 10th
year: 2002
3 authors: R. J. England | J.B. Rosenzweig | M.C. Thompson
abstract: We are developing a new beamline which will serve as a venue for future beam- plasma interaction experiments using the 14MeV electron beam produced by the UCLA Neptune 1.625-cell photoinjector and PWT linac. An examination of the first and second-order optics indicates that when certain nonlinear effects are minimized through the use of sextupole magnets, the longitudinal dispersion is dominated by a negative R 5 6- Simulations using the matrix transport code ELEGANT indicate that for an appropriately chirped initial beam, this beamline can be used to create a ramped picosecond to sub-picosecond beam that is ideal for driving large amplitude wake fields in a plasma and producing high transformer ratios.
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title: Plasma Wakefield Experiments
format: conference proceeding
conference: AAC 2002 10th
year: 2002
6 authors: N. Barov | M.C. Thompson | K. Bishofberger | J.B. Rosenzweig | H. Edwards | J. Santucci
abstract: We discuss the recent experiments in the field of Plasma Wakefield Acceleration (PWFA), with emphasis on the FNAL experiment. After completion of this work, the next round of experiments will need to push the envelope on accelerating gradient, interaction length, stability, and accelerated charge. We present theoretical results dealing with plasma accelerator performance in the limit of high driver charge, and short wavelengths. We comment on the impact of such results on both the afterburner (single module) and staged (multiple modules) approaches to plasma-based accelerators.
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title: Plasma electron fluid motion and wave breaking near a density transition
format: journal article
publisher: Physical Review E
year: 2002
3 authors: R. J. England | J.B. Rosenzweig | N. Barov
abstract: Recently, Suk, Barov, and Rosenzweig [Phys. Rev. Lett. 86, 1011 (2001)] proposed a scheme for trapping background electrons in a plasma wake field using a sudden downward transition in the background ion density, where the density transition length is small compared to the plasma skin depth. In the present paper we present a fluid dynamical description of this mechanism that is self-consistent up to the point of wave breaking. A one-dimensional nonlinear relativistic second-order differential equation is derived for the electron fluid velocity in Lagrangian coordinates. Numerical integrations of this equation are used to map out the regions of parameter space in which wave breaking occurs and to determine the extent of the downstream region of plasma involved in wave breaking. Comparisons with one-dimensional particle-in-cell (PIC) simulations show that the onset of trapping occurs at the parameter values where wave breaking begins in the fluid analysis, but that the downstream extent of plasma involved in wave breaking is not a reliable predictor of the number of trapped particles. The PIC simulations also reveal that particles initially located on the upstream side of the density transition may become trapped, although these particles do not participate in wave breaking in the fluid description.
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title: Space-charge effects in high brightness electron beam emittance measurements
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2002
4 authors: S. Anderson | J.B. Rosenzweig | G.P. Le Sage | J. K. Crane
abstract: The measurement of emittance in space-charge dominated, high brightness beam systems is investigated from conceptual, computational, and experimental viewpoints. As the self-field-induced collective motion in the low energy, high brightness beams emitted from photoinjector rf guns are more important in determining the macroscopic beam evolution than thermal spreads in transverse velocity; traditional methods for phase space diagnosis fail in these systems. We discuss the role of space charge forces in a traditional measurement of transverse emittance, the quadrupole scan. The mitigation of these effects by use of multislit- or pepper-pot-based techniques is explained. The results of a direct experimental comparison between quadrupole scanning and slit-based determination of the emittance of a 5 MeV high brightness electron beam are presented. These data are interpreted with the aid of both envelope and multiparticle simulation codes. It is shown that the ratio of the beam's beta function to its transverse plasma wavelength plays a central role in the quadrupole scan results. Methods of determining the presence of systematic errors in quadrupole scan data are discussed.
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title: Fundamental and Harmonic Microbunching Measurements in a High-Gain, Self-Amplified, Spontaneous Emission Free-Electron Laser
format: preprint
year: 2002
13 authors: A. Tremaine | X. J. Wang | M. Babzien | I. Ben-Zvi | M. Cornacchia | A. Murokh | H. D. Nuhn | R. Malone | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | Skaritka, J. | V. Yakimenko
abstract: The self-amplified, spontaneous emission free-electron laser (SASE-FEL) gain process is a collective instability which induces microbunching in the electron beam. Micro-bunching approaching unity at the fundamental FEL wavelength (845 nm), and its second harmonic, have been measured at the VISA FEL, at or near saturation. These measurements, which use the beam's coherent transition radiation (CTR) spectrum, are sompared to the predictions of FEL simulations. Comparison of shot-by-shot SASE and CTR signals firmly establishes the role of SASE in the development of microbunching harmonics.
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title: Electron Beam Production and Characterization for the PLEIADES Thomson X-Ray Source
format: conference proceeding
conference: AAC 2002 10th
year: 2002
13 authors: W. J. Brown | F. V. Hartemann | A. Tremaine | P. T. Springer | G.P. Le Sage | C. P. J. Barty | J.B. Rosenzweig | J. K. Crane | R. R. Cross | D. N. Fittinghoff | D. J. Gibson | D. R. Slaughter | S. Anderson
abstract: We report on the performance of an S-band RF photocathode electron gun and accelerator for operation with the PLEIADES Thomson x-ray source at LLNL. Simulations of beam production, transport, and focus are presented. It is shown that a 1 ps, 500 pC electron bunch with a normalized emittance of less than 5 Tcmm-mrad can be delivered to the interaction point. Initial electron measurements are presented. Calculations of expected x-ray flux are also performed, demonstrating an expected peak spectral brightness of 1020 photons/s/mm2/mrad2/0.1% bandwidth. Effects of RF phase jitter are also presented, and planned phase measurements and control methods are discussed.
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title: Inverse Free Electron Laser Experiment at the Neptune Laboratory
format: conference proceeding
conference: AAC 2002 10th
year: 2002
6 authors: P. Musumeci | C. Pellegrini | J.B. Rosenzweig | A. A. Varfolomeev | Tolmachev, S. | T. Yarovoi
abstract: We present an Inverse Free Electron Laser accelerator proposed for construction at the UCLA Neptune Laboratory. This experiment will use a 1 TW CO2 laser to accelerate through two strongly tapered undulators an electron beam from 16 MeV up to 5 MeV. The scheme proposed is the diffraction dominated IFEL interaction. The Raleigh range of the laser beam is about 2 cm, much shorter than the interaction length (the undulator length is 50 cm). In this regime adiabatic capture is possible in the first part of the undulator. In the focus region, we propose a solution to the problem of the dephasing between electrons and photons due to the
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title: Properties of an Ultra-Short Gain Length, Saturated, Self-Amplified Spontaneous Emission FEL
format: preprint
year: 2002
26 authors: A. Murokh | R. Agustsson | Pedro Frigola | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | A. Tremaine | M. Babzien | I. Ben-Zvi | E. Johnson | R. Malone | G. Rakowsky | Skaritka, J. | X. Wang | V. Yakimenko | L. Bertolini | J. M. Hill | G.P. Le Sage | M. Libkind | A. Toor | K. A. Van Bibber | R. Carr | M. Cornacchia | L. Klaisner | H. D. Nuhn | Ruland, R.
abstract: The VISA experiment, conducted at the BNL Accelerator Test Facility (ATF), has studied the properties of SASE FEL process in a saturating system. The experiment utilized a high brightness electron beam and a strong focusing undulator. Saturated gain greater than 108, with a power gain length below 18 cm, was obtained at 840 nm. Measurements of FEL gain, spectral and angular properties of SASE radiation are reported, and the results are compared to theory and to start-to-end simulations of the system. FEL performance was found critically dependent on the compression of the electron beam.
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title: Ultrafast materials probing with the LLNL Thomson X-ray source
format: conference proceeding
conference: Linear Accelerator Conference 2002
year: 2002
24 authors: A. Tremaine | S. Anderson | W. Brown | C. Barty | R. Cauble | J. Crane | H. Cynn | C. Ebbers | D. Fittinghoff | D. Gibson | F. Hartemann | I. Jovanovich | J. Kuba | G.P. Le Sage | A. McMahan | R. Minich | J. Moriarty | B. Remington | D. Slaughter | P. Springer | F. H. Steitz | C. S. Yoo | J.B. Rosenzweig | T. Ditmire
abstract: The use of short laser pulses to generate very high brightness, ultra short (fs to ps) x-ray pulses is a topic of great interest. In principle, femtosecond-scale pump-probe experiments can be used to temporally resolve structural dynamics of materials on the time scale of atomic motion. The development of sub?ps x-ray pulses will make possible a wide range of materials and plasma physics studies with unprecedented time resolution. PLEIADES (Picosecond Laser Electron Interaction for Dynamic Evaluation of Structures), the Thomson scattering project at LLNL, will provide such a novel x-ray source of high power using short laser pulses and a high brightness, relativistic electron bunch. The system is based on a 5 mm-mrad normalized emittance photoinjector, 100 MeV electron RF linac, and a 300 mJ, 35 fs solid-state laser system. PLEIADES will produce ultra fast pulses with x-ray energies (60 keV) capable of probing into high-Z metals.
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title: Beam extraction studies at 900 GeV using a channeling crystal
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2002
26 authors: R. Carrigan | D. Chen | G. Jackson | N. Mokhov | C.T. Murphy | S. I. Baker | S. A. Bogacz | D. B. Cline | S. Ramachandran | J. Rhoades | J.B. Rosenzweig | A. Asseev | R. A. Biryukov | A. Taratin | J. A. Ellison | A. Khanzadeev | T. Prokofieva | V. Samsonov | G. Solodov | B. Newberger | E. Tsyganov | H. J. Shih | W. Gabella | B. Cox | V. Golovatyuk | A. McManus
abstract: Luminosity-driven channeling extraction has been observed for the first time in a 900 GeV study at the Fermilab Tevatron. This experiment, Fermilab E853, demonstrated that useful TeV level beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors. Multipass extraction was found to increase the efficiency of the process significantly. The beam extraction efficiency was about 25%. Studies of time dependent effects found that the turn-to-turn structure was governed mainly by accelerator beam dynamics. Based on the results of this experiment, it is feasible to construct a parasitic 5?10 MHz proton beam from the Tevatron collider.
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title: Fundamental and harmonic microbunching in a high-gain self-amplified spontaneous-emission free-electron laser
format: journal article
publisher: Physical Review E
year: 2002
13 authors: A. Tremaine | X.J. Wang | M. Babzien | I. Ben-Zvi | M. Cornacchia | A. Murokh | H. D. Nuhn | R. Malone | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | J. Skaritka | V. Yakimenko
abstract: Electron beam microbunching in both the fundamental and second harmonic in a high-gain self-amplified spontaneous emission free-electron laser (SASE FEL) was experimentally characterized using coherent transition radiation. The microbunching factors for both modes (b1 and b2) approach unity, an indication of FEL saturation. These measurements are compared to the predictions of FEL simulations. The simultaneous capture of the microbunching and SASE radiation for individual micropulses correlate the longitudinal electron beam structure with the FEL gain.
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title: Experimental characterization of nonlinear harmonic radiation from a visible self-amplified spontaneous emission free-electron laser at saturation
format: journal article
publisher: Physical Review Letters
year: 2002
12 authors: A. Tremaine | X.J. Wang | M. Babzien | I. Ben-Zvi | M. Cornacchia | H. D. Nuhn | R. Malone | A. Murokh | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | V. Yakimenko
abstract: Nonlinear harmonic radiation was observed using the VISA self-amplified, spontaneous emission (SASE) free-electron laser (FEL) at saturation. The gain lengths, spectra, and energies of the three lowest SASE FEL modes were experimentally characterized. The measured nonlinear harmonic gain lengths and center spectral wavelengths decrease with harmonic number, n, which is consistent with nonlinear harmonic theory. Both the second and third nonlinear harmonics energies are about 1% of the fundamental energy. These experimental results demonstrate for the first time the feasibility of using nonlinear harmonic SASE FEL radiation to produce coherent, femtosecond X-rays. (33 References).
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title: Velocity bunching experiment at the Neptune Laboratory
format: conference proceeding
conference: AAC 2002 10th
year: 2002
5 authors: P. Musumeci | R. J. England | M.C. Thompson | R.B. Yoder | J.B. Rosenzweig
abstract: In this paper we describe the ballistic bunching compression experiment at the Neptune photoinjector at UCLA. We have compressed the beam by chirping the beam energy spectrum in a short S-band high gradient standing wave RF cavity and then letting the electrons undergo velocity compression in the subsequent rectilinear drift. Using a standard Martin Puplett interferometer for coherent transition radiation measurement, we have observed bunch length as short as 0.4 ps with compression ratio in excess of 10 for an electron beam of 7 MeV and charge up to 0.3 nC. We also measured slice transverse emittance via quad scan technique. The observed emittance growth agrees with the predictions and the simulations. Extension of this scheme to a future advanced accelerator injector system where solenoidal magnetic field can compensate the emittance growth is studied.
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title: A THz radiation driven IFEL as a phaselocked prebuncher for a plasma beat-wave accelerator
format: conference proceeding
conference: International Conference on Lasers 2001
year: 2002
6 authors: P. Musumeci | S. Ya. Tochitsky | C. E. Clayton | C. Joshi | C. Pellegrini | J.B. Rosenzweig
abstract: To obtain a high quality electron beam with small energy spread in the laser driven plasma accelerator, the electrons have to be prebunched at the scale of the plasma wavelength. We study the feasibility of an experiment where an inverse free electron laser (IFEL) is used to bunch the electron beam before the injection into a plasma beatwave accelerator. It is suggested to drive the IFEL prebuncher by a THz seed radiation phase-locked to the electromagnetic beatwave through difference frequency generation process in a nonlinear crystal. Design and numerical simulations for this experiment are presented.
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title: An undulator with nonadiabatic tapering for the IFEL project
format: conference proceeding
conference: FEL 2001 23rd
year: 2002
6 authors: A. A. Varfolomeev | S.V. Tolmachev | T. V. Yarovoi | P. Musumeci | C. Pellegrini | J.B. Rosenzweig
abstract: We describe the design of a planar undulator with unusually strong tapering, for the inverse FEL experiment (on the IFEL experiment at the UCLA Neptune Lab. Presented at the 2001 Particle Accelerator Conference, June 18-22, 2001, Chicago, Illinois) to be carried out in Neptune Lab. (Nucl. Instr. and Meth. A 410 (1998) 437) at UCLA. A powerful TW CO_2 laser will be used to accelerate electrons up to 50-60 MeV in 50 cm long undulator. A strong undulator tapering is needed because of the short Rayleigh length of the laser beam. Both the magnetic field and the undulator period are tapered to provide synchronicity of the laser beam interaction with a captured electron bunch along the whole undulator length. The most critical part of the undulator is the region near the laser focus. The main characteristics of the IFEL, such as the percentage of trapped electrons, energy of accelerated electrons and sensitivity to the laser focus transverse position, are given. The general principles of the design of this undulator construction can also be useful for high efficiency FEL amplifiers of intense laser modes.
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title: Photoinjector design for the LCLS
format: conference proceeding
conference: FEL 2001 23rd
year: 2002
16 authors: P.R. Bolton | Clendenin, J. E. | Dowell, D. H. | M. Ferrario | A.S. Fisher | Gierman, S. M. | Kirby, R. E. | P. Krejcik | Limborg, C. G. | Mulhollan, G. A. | D. C. Nguyen | D. T. Palmer | J.B. Rosenzweig | Schmerge, J. F. | L. Serafini | X.J. Wang
abstract: The design of the Linac Coherent Light Source assumes that a low-emittance, 1 nC, 10 ps beam will be available for injection into the 15 GeV linac. The proposed RF photocathode injector that will meet this requirement is based on a 1.6-cell S-band RF gun equipped with an emittance-compensating solenoid. The booster accelerator with a gradient of 25 MV/m is positioned at the beam waist coinciding with the first emittance maximum, i.e., the "new working point." The UV pulses required for cathode excitation will be generated by tripling the output of a Ti:sapphire laser system. Details of the design and the supporting simulations are presented. (12 References).
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title: Characterization of an 800 nm SASE FEL at saturation
format: conference proceeding
conference: FEL 2001 23rd
year: 2002
24 authors: A. Tremaine | Pedro Frigola | A. Murokh | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | M. Babzien | I. Ben-Zvi | E. Johnson | R. Malone | G. Rakowsky | Skaritka, J. | X. J. Wang | K. A. Van Bibber | L. Bertolini | J. M. Hill | G.P. Le Sage | M. Libkind | A. Toor | R. Carr | M. Cornacchia | L. Klaisner | H. D. Nuhn | Ruland, R.
abstract: Visible to Infrared SASE Amplifier is a free electron laser (FEL) designed to saturate at a radiation wavelength of 800 nm within a 4 m long, strong focusing undulator. A large gain is achieved by driving the FEL with 72 MeV, high brightness beam of BNL's accelerator test facility. We present measurements that demonstrate saturation in addition to the frequency spectrum of the FEL radiation. Energy, gain length and spectral characteristics are compared and shown to agree with simulation and theoretical predictions. (16 References).
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title: Start-to-end simulation for the LCLS X-ray FEL
format: conference proceeding
conference: FEL 2001 23rd
year: 2002
5 authors: S. Reiche | C. Pellegrini | J.B. Rosenzweig | P. Emma | P. Krejcik
abstract: X-ray FELs, such as the LCLS and TESLA FEL, require electron beams with large peak current and very small emittance. The X-ray peak power, temporal and spectral properties, depend significantly on details of the electron beam phase space distribution. The electron beam distribution is determined by many effects, as the emission process at the gun photo-cathode, bunch compression, acceleration and wakefields within the undulator. Although analytical results can give an estimate of the expected performance, the complexity of the electron beam generation, acceleration and compression can only be evaluated using a numerical simulation of all these processes, a start-to-end simulation. In this presentation we discuss the LCLS X-Ray FEL performance estimated by a start-to-end simulation, and we compare the results with those obtained using a simpler model. (20 References).
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title: Measuring FEL radiation properties at VISA-FEL
format: conference proceeding
conference: PAC 2001
year: 2001
25 authors: A. Murokh | R. Agustsson | Pedro Frigola | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | A. Tremaine | M. Babzien | I. Ben-Zvi | E. Johnson | R. Malone | G. Rakowsky | Skaritka, J. | X. J. Wang | K. A. Van Bibber | L. Bertolini | J. M. Hill | G.P. Le Sage | M. Libkind | A. Toor | R. Carr | M. Cornacchia | L. Klaisner | H. D. Nuhn | Ruland, R.
abstract: The VISA (Visible to Infrared SASE Amplifier) SASE free electron laser has been successfully operated at the Accelerator Test Facility (ATF) at BNL. High gain and saturation were observed at 840 nm. We describe here the diagnostic system, experimental procedures and data reduction algorithms, as the FEL performance was measured along the length of the undulator. We also discuss selected spectral radiation measurements. (10 References).
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title: Dynamics of a Driver Beam Propagating in an Underdense Plasma with a Downward Density Transition
format: conference proceeding
conference: PAC 2001
year: 2001
7 authors: Suk, H. | N. Barov | R. J. England | E. Esarey | G. Kim | J.B. Rosenzweig | M.C. Thompson
abstract: When a short electron beam propagates in an underdense plasma (plasma density n_p < beam density n_b) with a downward density transition, it is known that some background plasma electrons are trapped and accelerated by the plasma wakefield[1]. Beam quality of the trapped plasma electrons is severely affected by the wakefield that is generated by the driving electron beam, so dynamics and instabilities of the driver beam are very important. In this paper, we present some simulation results on the self-trapping and driver beam dynamics.
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title: Commissioning of the Neptune photoinjector
format: conference proceeding
conference: PAC 2001
year: 2001
9 authors: S. Boucher | Burke, A. | Loh, M. | P. Musumeci | J.B. Rosenzweig | M.C. Thompson | S. Anderson | R. Agustsson | R. J. England
abstract: The status of the RF photoinjector in the Neptune advanced accelerator laboratory is discussed. The components of the photoinjector: the RF gun and booster linac, chicane compressor, and beam diagnostic systems are described. Measurement techniques used to diagnose the short pulse length, high brightness beam are detailed and measurements of emittance and pulse compression are given. The effect of the pulse compressor on transverse emittance is explored. (11 References).
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title: Proposal for a IR Waveguide SASE FEL at the PEGASUS Injector
format: conference proceeding
conference: PAC 2001
year: 2001
3 authors: Sven Reiche | J.B. Rosenzweig | S. Telfer
abstract: Free Electron Lasers up to the visible regime are dominated by diffraction effects, resulting in a radiation size much larger than the electron beam. Thus the effective field amplitude at the location of the electron beam, driving the FEL process, is reduced. By using a waveguide, the radiation field is confined within a smaller aperture and an enhancement of the FEL performance can be expected. The PEGASUS injector at UCLA will be capable to provide the brilliance needed for an IR SASE FEL. The experiment PERSEUS (Power Enhanced Radiation Source Experiment Using Structures) is proposed to study the physics of a waveguide SASE FEL in a quasi 1D environment, where diffraction effects are strongly reduced as it is the case only for future FELs operating in the VUV and X-ray regime. The expected FEL performance is given by this presentation.
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title: Transition radiation for uneven, limited surfaces
format: conference proceeding
conference: PAC 2001
year: 2001
2 authors: Sven Reiche | J.B. Rosenzweig
abstract: In the most common approach to modeling transition radiation, the annihilation of the incident particle with its image particle at the metallic boundary is calculated. This is valid only for ideal planar boundaries, and is not applicable if the surface is modulated, rough or limited in the transverse dimension. In this paper, we show results obtained by replacing the image current with the induced surface charge and surface distributions. Special problems such as a modulated surface are analytically solved and compared to a numerical simulation. Implications for experimental use of transition radiation-based beam monitors are discussed. (9 References).
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title: Monitoring and manipulation of sub-picosecond beams
format: conference proceeding
conference: PAC 2001
year: 2001
1 author: J.B. Rosenzweig
abstract: In cutting-edge applications such as advanced accelerators and free-electron lasers, very high brightness beams of duration shorter than a picosecond are required. Further, these applications demand specific types of longitudinal beam profiles, such as pulse trains, and ramped pulses. The production of such types of beams present challenges both in technique, and in the instrumentation required to verify the method employed. The techniques for producing such short beams which have received the most investigation in recent years include chicane compression, and modulation via free-electron laser mechanism and its inverse. We discuss the principles and relevant single particle and collective effects which impact their performance. We review progress in implementing these schemes, as well as newer concepts such as relativistic velocity bunching and use of negative R_56 compressors. We also discussed the challenges in diagnosing these state-of-the-art beam systems.
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title: Beam-plasma interaction experiments at the UCLA Neptune Laboratory
format: conference proceeding
conference: PAC 2001
year: 2001
5 authors: M.C. Thompson | C. E. Clayton | R. J. England | J.B. Rosenzweig | Suk, H.
abstract: We are currently planning several beam-plasma interaction experiments using the high quality 16 MeV electron beam produced by the Neptune 1.625-cell photoinjector and PWT linac. The underdense (n_b > n_0) plasma lens experiment will examine the focusing of a 4 nC beam of 30 psec pulse duration as it passes through a thin 2 cm Ar plasma lens. We are also developing a negative R_56 compressor beamline that will allow us to create ramped sub-picosecond beams of a shape well suited for driving large amplitude plasma wake fields and producing high transformer ratios. Simulations made using the 2-1/2 dimensional particle-in-cell code MAGIC indicate that we could use these ramped beams to produce fields of up to 10 GeV/m in a 10(16) cm(-3) plasma. Ramped beams are also suitable for driving plasma density gradient trapping experiments. When such a beam passes through a region where the plasma density drops suddenly the fast variation of the wake fields traps several pC of plasma electrons in the accelerating portion of the wake field.
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title: Limitations on Measuring a Transverse Profile of Ultradense Electron Beams with Scintillators
format: conference proceeding
conference: PAC 2001
year: 2001
5 authors: A. Murokh | J.B. Rosenzweig | Ben-Zvi, I. | X. Wang | V. Yakimenko
abstract: As the high-brightness electron beams become denser and reach sub-100 um sizes, a resolution of the transverse profile diagnostics become an important issue. The applicability of the traditional scintillators as the diagnostics for most generic transverse properties of small dense beams is questionable. Recently, a YAG:Ce single crystal was used successfully, but studies indicated the presence of saturation effects. At BNL-ATF (Accelerator Test Facility) we have generated ultra-small beams, and continued an experimental work to further illuminate the nature of YAG:Ce saturation. We have also evaluated alternative diagnostics, such as LuAG:Ce. Imaging properties of various diagnostics were studied, including measurements of emission spectra.
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title: Development of an X-Band PWT Photoinjector
format: conference proceeding
conference: PAC 2001
year: 2001
5 authors: D. Newsham | Luo, Y. | Zeng, J. | D. Yu | J.B. Rosenzweig
abstract: Development of an X-band Plane-Wave-Transformer (PWT), integrated photoinjector continues. Modifications of the end-cell design in this two-section device allow for simultaneous frequency and phase tuning of the accelerating field, thus preventing deceleration at the drift region that separates the two sections. The Los Alamos version of PARMELA is used to determine the expected performance parameters from the final design.
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title: Emittance measurements of the space charge dominated Thomson source photoinjector
format: conference proceeding
conference: PAC 2001
year: 2001
4 authors: S. Anderson | J.B. Rosenzweig | G.P. Le Sage | J. Crane
abstract: The photocathode rf gun test facility in Livermore National Laboratory's Thomson source is described. The quadrupole scan and slit based emittance measurement techniques are used to measure the emittance of the space charge dominated beam. Experimental results are compared with simulation and theoretical calculations. (10 References).
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title: Ultra high-gradient energy loss by a pulsed electron beam in a plasma
format: conference proceeding
conference: PAC 2001
year: 2001
9 authors: N. Barov | K. Bishofberger | J.B. Rosenzweig | J.P. Carneiro | P. Colestock | H. Edwards | Fitch, M. J. | W. Hartung | J. Santucci
abstract: The plasma wake-field mechanism can be used to couple energy at a high rate from a bunched electron beam into a plasma wave. We will present results from the Fermilab A0 facility where a beam with an initial energy of 14 MeV passes through the plasma to emerge with a much broader energy spread, spanning from a low of 3 MeV to a high of over 20 MeV. Over the 8 cm length of the 10(14) cm(-3) plasma, this implies a 140 MeV/m deceleration and 72 MeV/m acceleration gradient. (12 References).
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title: Commissioning of the UCLA PEGASUS Photoinjector Laboratory
format: conference proceeding
conference: PAC 2001
year: 2001
5 authors: S. Telfer | Sven Reiche | J.B. Rosenzweig | Pedro Frigola | G. Andonian
abstract: The PEGASUS Photoinjector has been commissioned at UCLA. The Plane Wave Transformer Photoinjector provides a high-brightness 17 MeV beam that will be used for numerous beam-radiation studies. Some of these will include SASE FEL, transition radiation from non-standard surfaces, and monochromatic x-ray production via PXR and Thompson scattering.
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title: Start-to-end simulation for the LCLS X-ray FEL
format: conference proceeding
conference: PAC 2001
year: 2001
5 authors: Sven Reiche | C. Pellegrini | J.B. Rosenzweig | P. Emma | P. Krejcik
abstract: X-ray FELs, such as the LCLS and TESLA FEL, require electron beams with large peak current and very small emittance. The X-ray peak power, temporal and spectral properties, depend significantly on details of the electron beam phase space distribution. The electron beam distribution is determined by many effects, as the emission process at the gun photo-cathode, bunch compression, acceleration and wakefields within the undulator. Although analytical results can give an estimate of the expected performance, the complexity of the electron beam generation, acceleration and compression can only be evaluated using a numerical simulation of all these processes, a start-to-end simulation. In this presentation we discuss the LCLS X-Ray FEL performance estimated by a start-to-end simulation, and we compare the results with those obtained using a simpler model. (19 References).
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title: On the IFEL experiment at the UCLA Neptune Lab
format: conference proceeding
conference: PAC 2001
year: 2001
6 authors: P. Musumeci | C. Pellegrini | J.B. Rosenzweig | A. A. Varfolomeev | Tolmachev, S. | T. Yarovoi
abstract: We present an inverse free electron laser accelerator proposed for construction at the UCLA Neptune Lab. This experiment will use a 1TW CO/sub 2/ laser to accelerate through two strongly tapered undulators an electron beam from 16 MeV up to 55 MeV. The scheme proposed is the diffraction dominated IFEL interaction. The Raleigh range of the laser beam is about 2 cm, much shorter than the interaction length (the undulator length is 50 cm). In this regime adiabatic capture is possible in the first part of the undulator. In the focus region, we propose a solution to the problem of the dephasing between electrons and photons due to the Guoy phase shift. Ponderomotive effects and implications for tolerances are also studied. (13 References).
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title: Saturation measurements of a visible SASE FEL
format: conference proceeding
conference: PAC 2001
year: 2001
14 authors: A. Tremaine | P. Frigola | A. Murokh | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | M. Babzien | I. Ben-Zvi | E. Johnson | R. Malone | G. Rakowsky | Skaritka, J. | X. J. Wang | V. Yakimenko
abstract: VISA (visible to infrared SASE amplifier) is an FEL designed to obtain high gain at a radiation wavelength of 800 nm. Large gain is achieved by driving the FEL with the 71 MeV, high brightness beam of the Accelerator Test Facility (ATF) and using a novel, strong focusing, 4 m long undulator with a gap of 6 mm and a period of 1.8 cm. We report measurements of exponential gain, saturation, and spectra of the FEL radiation intensity. (11 References).
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title: Plasma Electron Trapping and Acceleration in a Plasma Wake Field Using a Density Transition
format: journal article
publisher: Physical Review Letters
year: 2001
4 authors: Suk, H. | N. Barov | J.B. Rosenzweig | E. Esarey
abstract: A new scheme for plasma electron injection into an acceleration phase of a plasma wake field is presented. In this scheme, a single, short electron pulse travels through an underdense plasma with a sharp, localized, downward density transition. Near this transition, a number of background plasma electrons are trapped in the plasma wake field, due to the rapid wavelength increase of the induced wake wave in this region. The viability of this scheme is verified using two-dimensional particle-in-cell simulations. To investigate the trapping and acceleration mechanisms further, a 1D Hamiltonian analysis, as well as 1D simulations, has been performed, with the results presented and compared.
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title: ORION: An Advanced Accelerator Facility at SLAC
format: conference proceeding
conference: PAC 2001
year: 2001
13 authors: D. T. Palmer | E. Colby | M. Hogan | R. Noble | R. H. Siemann | Spencer, J. | D. Walz | C. Joshi | W. Mori | J.B. Rosenzweig | T. Katsouleas | P. Muggli | R. Byer
abstract: Extending the center-of-mass energy frontier for high-energy physics depends on the research and development that is conducted now in the area of advanced accelerator physics and technology. In this article, we present the design and beam dynamics simulations for the emittance-compensated, RF photoinjector of the ORION Facility. (4 References).
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title: Visible-infrared self-amplified spontaneous emission amplifier free electron laser undulator
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2001
17 authors: R. Carr | M. Cornacchia | P. Emma | H. D. Nuhn | B. Poling | R. Ruland | E. Johnson | G. Rakowsky | J. Skaritka | S. Lidia | P. Duffy | M. Libkind | Pedro Frigola | A. Murokh | C. Pellegrini | J.B. Rosenzweig | A. Tremaine
abstract: The visible-infrared self-amplified spontaneous emission amplifier (VISA) free electron laser (FEL) is an experimental device designed to show self-amplified spontaneous emission (SASE) to saturation in the near infrared to visible light energy range. It generates a resonant wavelength output from 800?600 nm, so that silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is designed to show how SASE FEL theory corresponds with experiment in this wavelength range, using an electron beam with emittance close to that planned for the future Linear Coherent Light Source at SLAC. VISA comprises a 4 m pure permanent magnet undulator with four 99 cm segments, each of 55 periods, 18 mm long. The undulator has distributed focusing built into it, to reduce the average beta function of the 70?85 MeV electron beam to about 30 cm. There are four FODO cells per segment. The permanent magnet focusing lattice consists of blocks mounted on either side of the electron beam, in the undulator gap. The most important undulator error parameter for a free electron laser is the trajectory walk-off, or lack of overlap of the photon and electron beams. Using pulsed wire magnet measurements and magnet shimming, we were able to control trajectory walk-off to less than
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title: Production and synchronization of electron beams from RF photoinjector/compressor systems for ultra-fast applications
format: conference proceeding
conference: AAC 2000 9th
year: 2001
2 authors: M.C. Thompson | J.B. Rosenzweig
abstract: The RF photoinjector, when coupled with a magnetic pulse compression system, is now an ubiquitous tool for production of sub-picosecond electron beam pulses which are to be used in advanced accelerator and light source experiments. As the time-scale for both pulse lengths and synchronization to external systems approaches the femtosecond level, a clear understanding of the longitudinal dynamics of the electron injector is required. This paper presents an analysis of the longitudinal beam dynamics of electron bunches in the photoinjector/compressor system from birth at the photocathode, through their initial violent acceleration in the RF gun, and subsequent phase space manipulation in the post-acceleration linac and magnetic chicane. The phenomena of phase focusing due to RF forces, and defocusing due to longitudinal space-charge, are discussed, as is the process of magnetic pulse compression. The issues relevant to synchronization of electron pulses with external lasers are examined, using the examples of beat-wave acceleration and Compton light sources, and solutions involving appropriate compressor configurations are proposed. Diagnosis of the relevant physical effects in such schemes is discussed.
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title: Initial gain measurements of an 800 nm SASE FEL, VISA
format: conference proceeding
conference: FEL 2000 22nd
year: 2001
26 authors: P. Frigola | A. Murokh | P. Musumeci | C. Pellegrini | Sven Reiche | J.B. Rosenzweig | A. Tremaine | M. Babzien | I. Ben-Zvi | E. Johnson | R. Malone | G. Rakowsky | Skaritka, J. | X. J. Wang | K. A. Van Bibber | L. Bertolini | J. M. Hill | G.P. Le Sage | M. Libkind | A. Toor | R. Carr | M. Cornacchia | L. Klaisner | H. D. Nuhn | Ruland, R. | D. C. Nguyen
abstract: The visible to infrared SASE amplifier (VISA) FEL is designed to obtain high gain at a radiation wavelength of 800 nm. The FEL uses the high brightness electron beam of the accelerator test facility (ATF), with energy of 72 MeV. VISA uses a novel, 4 m long, strong focusing undulator with a gap of 6 mm and a period of 1.8 cm. To obtain large gain the beam and undulator axis have to be aligned to better than 5 mu m. Results from initial measurements on the alignment, gain, and spectrum will be presented and compared to theoretical calculations and simulations. (10 References).
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title: Commissioning and measurements of the Neptune photo-injector
format: conference proceeding
conference: AAC 2000 9th
year: 2001
6 authors: S. Anderson | Loh, M. | P. Musumeci | J.B. Rosenzweig | Suk, H. | M.C. Thompson
abstract: The photo-injector for the Neptune Advanced Accelerator Laboratory is introduced. Its component parts, including the radio frequency gun, photo-cathode drive laser system, booster linac, RF system, chicane compressor, beam diagnostics, and control system are described. The injector is designed to produce high brightness, short pulse electron beams. Measurements of the photo-injector beams including quantum efficiency, emittance, pulse length, and pulse compression are presented. (21 References).
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title: Chicane compressor development for BNL ATF- applications to SASE FEL
format: conference proceeding
conference: FEL 2000 22nd
year: 2001
2 authors: R. Agustsson | J.B. Rosenzweig
abstract: A chicane compressor is being designed and constructed at UCLA for implementation at the BNL Accelerator Test Facility. The beam optics, including collective fields, and expected performance of the device has been simulated using TRACE3D and ELEGANT. Based on these studies, as well as constraints due to downstream ATF optics, the chicane magnet specifications were determined. The dipole magnets were designed using AMPERES 3D magnetostatic modeling, and have been constructed. Implementation of this device at the ATF, as well as initial physics experiments on coherent synchrotron radiation emission (and associated emittance growth) at 70 MeV, and expected performance enhancement of the VISA SASE FEL experiment, are discussed.
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title: Proposal for a IR waveguide SASE FEL at the PEGASUS injector
format: conference proceeding
conference: FEL 2000 22nd
year: 2001
3 authors: Sven Reiche | J.B. Rosenzweig | S. Telfer
abstract: Free Electron Lasers up to the visible regime are dominated by diffraction effects, resulting in a radiation size much larger than the electron beam. Thus the effective field amplitude at the location of the electron beam, driving the FEL process, is reduced. By using a waveguide, the radiation field is confined within a smaller aperture and an enhancement of the FEL performance can be expected. The PEGASUS injector at UCLA will be capable to provide the brilliance needed for an IR SASE FEL. The experiment Power Enhanced Radiation Source Experiment Using Structures (PERSEUS) is proposed to study the physics of a waveguide SASE FEL in a quasi I D environment, where diffraction effects are strongly reduced as it is the case only for future FELs operating in the VUV and X-ray regime. The expected FEL performance is given by this presentation.
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title: The PEGASUS free electron laser laboratory
format: conference proceeding
conference: FEL 2000 22nd
year: 2001
4 authors: S. Telfer | Sven Reiche | J.B. Rosenzweig | P. Frigola
abstract: The PEGASUS (Photoelectron Generated Amplified Spontaneous Radiation Source) free electron laser laboratory is currently being commissioned at UCLA.
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title: RF photoinjector development for a short-pulse, hard X-ray Thomson scattering source
format: conference proceeding
conference: AAC 2000 9th
year: 2001
6 authors: G.P. Le Sage | S. G. Anderson | T. E. Cowan | J. K. Crane | T. Ditmire | J.B. Rosenzweig
abstract: An important motivation in the development of the next generation X-ray light sources is to achieve picosecond and sub-ps pulses of hard X-rays for dynamic studies of a variety of physical, chemical anti biological processes. Present hard X-ray sources are either pulse-width or intensity limited, which allows ps-scale temporal resolution only for signal averaging of highly repetitive processes. A much faster and brighter hard X-ray source is being developed at LLNL, based on Thomson scattering of fs-laser pulses by a relativistic electron beam, which will enable X-ray characterization of the transient structure of a sample in a single shot. Experimental and diagnostic techniques relevant to the development of next generation sources including the Linac Coherent Light Source can be tested with the Thomson scattering hard X-ray source. This source will combine an RF photoinjector with a 100 MeV S-band linac. The photoinjector and linac also provide an ideal test-bed for examining space-charge induced emittance growth effects. A program of beam dynamics and diagnostic experiments are planned in parallel with Thomson source development. Our experimental progress and future plans will be discussed.
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title: Optimization of an x-ray SASE-FEL
format: conference proceeding
conference: FEL 2000 22nd
year: 2001
7 authors: C. Pellegrini | Sven Reiche | J.B. Rosenzweig | C. Schroeder | A. A. Varfolomeev | Tolmachev, S. | H. D. Nuhn
abstract: The most important characteristics of an X-ray SASE-FEL are determined by the electron beam energy, transverse and longitudinal emittance, and by choice of the undulator period, field, and gap. Among them are the gain and saturation length, the amount and spectral characteristics of the spontaneous radiation, the wake fields due to the vacuum pipe. The spontaneous radiation intensity is very large in all X-ray SASE-FELs now being designed, and it contributes to the final electron beam energy spread, thus affecting the gain. It also produces a large background for the beam and radiation diagnostics instrumentation. The wake fields due to the resistivity and roughness of the beam pipe through the undulator, also affects the beam 6-dimensional phase space volume, and thus the gain and the line width. In this paper, we discuss ways to optimize the FEL when considering all these effects. In particular we consider and discuss the use of a hybrid iron-permanent magnet helical undulator to minimize some of these effects, and thus optimize the FEL design.
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title: Trapping of background plasma electrons in a beam-driven plasma wake field using a downward density transition
format: conference proceeding
conference: AAC 2000 9th
year: 2001
4 authors: Suk, H. | N. Barov | J.B. Rosenzweig | E. Esarey
abstract: Trapping of background plasma electrons by a beam-driven plasma wake field is studied as a new self-injection method. In this scheme, a short electron beam pulse is sent through an underdense plasma with a downward density transition and some background plasma electrons are trapped by the strong wake field due to the sudden increase of the wake wave wavelength at the density transition. Two-dimensional PIC (Particle-In-Cell) simulations show that a significant amount of plasma electrons are trapped and accelerated to a higher energy than the driving beam energy. Furthermore, the trapped-beam quality is fairly good. In this paper, the 2-D simulation results, dynamics of the trapped beam and the driving beam, and the proposed experiment for the UCLA Neptune Laboratory are described. (15 References).
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title: Intra-undulator measurements at VISA FEL
format: conference proceeding
conference: FEL 2000 22nd
year: 2001
11 authors: A. Murokh | P. Frigola | C. Pellegrini | J.B. Rosenzweig | A. Tremaine | E. Johnson | X.J. Wang | V. Yakimenko | L. Klaisner | H-D. Nuhn | A. Toor
abstract: We describe a diagnostics system developed, to measure exponential gain properties and the electron beam dynamics inside the strong focusing 4-m long undulator for the VISA (Visible to Infrared SASE Amplifier) FEL. The technical challenges included working inside the small undulator gap, optimising the electron beam diagnostics in the high background environment of the spontaneous undulator radiation, multiplexing and transporting the photon beam. Initial results are discussed.
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title: Optimization of an X-ray SASE FEL
format: conference proceeding
conference: ICFA Beam Dynamics Workshop on Physics of, and Science with, the X-Ray Free-Electron Laser 19th
year: 2001
7 authors: C. Pellegrini | Sven Reiche | J.B. Rosenzweig | C. Schroeder | A. A. Varfolomeev | Tolmachev, S. | H-D. Nuhn
abstract: The most important characteristics of an X-ray SASE-FEL are determined by the electron beam energy, transverse and longitudinal emittance, and by choice of the undulator period, field, and gap. Among them are the gain and saturation length, the amount and spectral characteristics of the spontaneous radiation, the wake fields due to the vacuum pipe. The spontaneous radiation intensity is very large in all X-ray SASE-FELs now being designed, and it contributes to the final electron beam energy spread, thus affecting the gain. It also produces a large background for the beam and radiation diagnostics instrumentation. The wake fields due to the resistivity and roughness of the beam pipe through the undulator, also affects the beam 6-dimensional phase space volume, and thus the gain and the line width. In this paper, we discuss ways to optimize the FEL when considering all these effects. In particular we consider and discuss the use of a hybrid iron-permanent magnet helical undulator to minimize some of these effects, and thus optimize the FEL design.
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title: New design study and related experimental program for the LCLS RF photoinjector
format: conference proceeding
conference: EPAC 2000
year: 2000
11 authors: M. Ferrario | P.R. Bolton | Clendenin, J. E. | Dowell, D. H. | Gierman, S. M. | M. E. Hernandez | D. C. Nguyen | D. T. Palmer | J.B. Rosenzweig | Schmerge, J. F. | L. Serafini
abstract: We report the results of a recent beam dynamics study, motivated by the need to redesign the LCLS photoinjector, that lead to the discovery of a new effective working point for a split RF photoinjector. We consider the emittance compensation regime of a space charge beam: by increasing the solenoid strength, the emittance evolution shows a double minimum behavior in the drifting region. If the booster is located where the relative emittance maximum and the envelope waist occur, the second emittance minimum can be shifted to the booster exit and frozen at a very low level (0.3 mm-mrad for a 1 nC flat top bunch), to the extent that the invariant envelope matching conditions are satisfied. Standing Wave Structures or alternatively Traveling Wave Structures embedded in a Long Solenoid are both candidates as booster linac. A careful measurement of the emittance evolution as a function of position in the drifting region is necessary to verify the computation and to determine experimentally the proper position of the booster cavities. The new design study and supporting experimental program under way at the SLAC Gun Test Facility are discussed.
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title: Nonequilibrium transverse motion and emittance growth in ultrarelativistic space-charge dominated beams
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2000
2 authors: S. Anderson | J.B. Rosenzweig
abstract: The transverse dynamics of space-charge dominated beams are investigated both analytically and computationally, in order to understand the mechanisms for emittance oscillations and growth due to nonlinear space-charge fields. This work explores the role of space-charge dominated equilibrium and its relationship to phase space wave breaking, which is responsible for the irreversible emittance growth in these systems. The physics of both coasting and accelerating beams are examined in order to illuminate the most effective approaches to beam handling during the emittance compensation process as well as during subsequent beam transport. These results are discussed within the context of recent ultrahigh brightness RF photoinjector designs. (20 References).
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title: Initial operation of S-band plane wave transformer photoinjector
format: conference proceeding
conference: APS April Meeting
year: 2000
4 authors: X. Ding | C. Pellegrini | J.B. Rosenzweig | S. Telfer
abstract: An integrated S-Band RF photoinjector based on the plane wave transformer (PWT) is being built and operated in the Particle Beam Physics Laboratory at UCLA. This novel structure integrates a photocathode directly into a PWT Linac making the structure simple and compact. Due to the strong coupling between each adjacent cell, this structure is relatively easy to fabricate and operate. This photoinjector can provide high brightness beams at energies of 15 to 20MeV, with emittance less than 1mm-mrad at charge of 1 nC. These short-pulse beams can be used in various applications: space charge dominated beam physics studies, plasma lenses, plasma accelerators, free-electron laser microbunching techniques, and SASE-FEL physics studies. It will also provide commercial opportunities in chemistry, biology and medicine. The initial operation of the PWT photoinjector with high RF power is described. A comparation of experimental result and theoretical design is also discussed.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma
format: preprint
year: 2000
3 authors: N. Barov | J.B. Rosenzweig | M.C. Thompson
abstract: There has been much interest in the regime of plasma wake-field acceleration (PWFA) having ultra-high fields, and associated nonlinear plasma motion. With an exact analytical approach, we examine here a fundamental limit of PWFA excitation, by an infinitesimally short relativistic bunched beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams.
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title: Non-equilibrium transverse motion and emittance growth in space-charge dominated beams
format: conference proceeding
conference: APS April Meeting
year: 2000
2 authors: S. Anderson | J.B. Rosenzweig
abstract: The transverse dynamics of space-charge dominated beams are investigated both analyitically and computationally, in order to understand the mechanisms for emittance oscillations and growth due to nonlinear space-charge fields. This work explores the role of space-charge dominated equilibrium and its relationship to phase space wave-breaking, which is responsible for the irreversible emittance growth in these systems. The physics of both coasting and accelerating beams are examined, in order to illuminate the most effective approaches to beam handling during the emittance compensation process, as well as during subsequent beam transport.
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title: Electron Beam Photocathode Cleaning
format: conference proceeding
conference: APS April Meeting
year: 2000
7 authors: M.C. Thompson | S. Anderson | Loh, M. | P. Musumeci | J.B. Rosenzweig | Suk, H. | D. T. Palmer
abstract: We are experimenting with low energy electron beams as a means of cleaning and improving the quantum efficiency of metallic photocathodes. Electron beam surface cleaning has been used successfully in electron cooling devices at Fermilab (S. Nagaitsev) and Novosibirsk (A.N. Sharapa and A.V. Shemyakin). The cooling device data indicates that a 2 mA h/cm2 specific dose of 3 keV electrons on the surface of the photocathode will produce a surface with an outgas rate at least one order of magnitude lower than a 24 hour 400
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title: Highlights of AAC 2000 Workshop
format: conference proceeding
conference: Linear Accelerator Conference 2000
year: 2000
1 author: J.B. Rosenzweig
abstract: The Advanced Accelerator Concepts 2000 (AAC2K) Workshop was held in Santa Fe in June, 2000, and included a wide array of conceptual and theoretical advances at the frontier of accelerator physics. This paper reviews the highlights of the workshop, with subjects ranging from acceleration using lasers, plasmas and microstructures, to the beam physics of muon colliders. Particular emphasis is given to the topics which are relevant to research at existing linear accelerator facilities, and the effect of this research on the capabilities of such facilities.
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title: Plasma Electron Trapping and Acceleration in a Plasma Wake Field Using a Density Transition
format: preprint
year: 2000
4 authors: E. Esarey | H. Suk | N. Barov | J.B. Rosenzweig
abstract: A new scheme for plasma electron injection into an acceleration phase of a plasma wakefield is presented. In this scheme, a short single electron beam bunch is sent through an underdense plasma with a sharp, localized downward density transition. Near this transition, a number of background plasma electrons are trapped in the plasma wake field due to the rapid wavelength increase of the wake wave in this region. The viability of this scheme is verified using two-dimensional particle-in-cell (PIC) simulations. To investigate the trapping and acceleration mechanism further, a 1-D Hamiltonian analysis as well as 1-D simulations have been performed, with the results are presented and compared.
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title: Observation of plasma wakefield acceleration in the underdense regime
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2000
5 authors: N. Barov | J.B. Rosenzweig | M. E. Conde | W. Gai | J. G. Power
abstract: Initial experiments which have explored the physics of the underdense (blowout) regime of the plasma wakefield accelerator (PWFA) at the Argonne Wakefield Accelerator facility are reported. In this regime, the relativistic electron beam is denser than the plasma, causing the beam channel to completely rarefy, and leaving a high quality accelerating region which also contains a uniform ion column. This ion column in turn allows the drive and accelerating beams to be well guided over many initial beam beta-function lengths. The results of these experiments, which have taken place over several years, are reviewed. Notable achievements in the course of these studies include the creation and measurement of drive and witness beam generated in an rf photoinjector, as well as previously published studies on drive beam guiding in the underdense regime. In addition, these experiments allowed measurement of both beam energy loss and gain, at a maximum average rate of 25 MeV/m in this regime of the PWFA, which is consistent with a peak acceleration gradient of 62 MeV/m in the excited waves. Difficulties associated with this type of experiment are discussed, as are prospects for mitigating these difficulties and achieving high gradient acceleration in planned future experiments.
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title: Commissioning of the Neptune Photoinjector
format: conference proceeding
conference: APS April Meeting
year: 2000
13 authors: S. Anderson | J.B. Rosenzweig | Burke, A. | X. Ding | Loh, M. | P. Musumeci | C. Pellegrini | Suk, H. | M.C. Thompson | C. Clayton | C. Joshi | Marsh, K. | P. Muggli
abstract: The status of the commissioning of the rf photoinjector in the Neptune advanced accelerator laboratory is discussed. The component parts of the photoinjector, the rf gun, photocathode drive laser system, booster linac, rf system, chicane compressor, beam diagnostics systems, and control system are described. Recent improvements in the rf gun, rf timing, and chicane compressor systems are detailed. This injector is designed to produce short pulse length, high brightness electron beams. Experiments planned for the immediate future are described. Initial measurements of various beam parameters are presented.
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title: First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength
format: journal article
publisher: Physical Review Letters
year: 2000
145 authors: J. Andruszkow | B. Aune | V. Ayvazyan | N. Baboi | R. Bakker | V. Balakin | D. Barni | A. Bazhan | M. Bernard | A. Bosotti | J. C. Bourdon | W. Brefeld | R. Brinkmann | S. Buhler | J. P. Carneiro | M. Castellano | P. Castro | L. Catani | S. Chel | Y. Cho | S. Choroba | E. R. Colby | W. Decking | P. Den Hartog | M. Desmons | M. Dohlus | D. Edwards | H. T. Edwards | B. Faatz | J. Feldhaus | M. Ferrario | M. J. Fitch | K. Floettman | M. Fouaidy | A. Gamp | T. Garvey | C. Gerth | M. Geitz | E. Gluskin | V. Gretchko | U. Hahn | W. H. Hartung | D. Hubert | M. Huening | R. Ischebek | M. Jablonka | J. M. Joly | M. Juillard | T. Junquera | P. Jurkiewicz | A. Kabel | J. Kahl | H. Kaiser | T. Kamps | V. V. Katelev | J. L. Kirchgessner | M. Koerfer | L. Kravchuk | G. Kreps | J. Krzywinski | T. Lokajczyk | R. Lange | B. Leblond | M. Leenen | J. Lesrel | M. Liepe | A. Liero | T. Limberg | R. Lorenz | H. H. Lu | F. H. Lu | C.4 Magne | M. Maslov | G. Materlik | A. Matheisen | J. Menzel | P. Michelato | W. D. Moeller | A. Mosnier | U. C. Mueller | O. Napoly | A. Novokhatski | M. Omeich | H. S. Padamsee | C. Pagani | F. Peters | B. Petersen | P. Pierini | J. Pflueger | P. Piot | B. Phung Ngoc | L. Plucinski | D. Proch | K. Rehlich | Sven Reiche | D. Reschke | I. Reyzl | J.B. Rosenzweig | J. Rossbach | S. Roth | E. L. Saldin | W. Sandner | Z. Sanok | H. Schlarb | G. Schmidt | P. Schmueser | J. R. Schneider | E. A. Schneidmiller | H. J. Schreiber | S. Schreiber | P. Schuett | J. Sekutowicz | L. Serafini | D. Sertore | S. Setzer | S. Simrock | B. Sonntag | B. Sparr | F. Stephan | V. A. Sytchev | S. Tazzari | F. Tazzioli | M. Tigner | M. Timm | M. Tonutti | E. Trakhtenberg | R. Treusch | D. Trines | V. Verzilov | T. Vielitz | V. Vogel | G. v. Walter | R. Wanzenberg | T. Weiland | H. Weise | J. Weisend | M. Wendt | M. Werner | M. M. White | I. Will | S. Wolff | M. V. Yurkov | K. Zapfe | P. Zhogolev | F. Zhou
abstract: We present the first observation of self-amplified spontaneous emission (SASE) in a free-electron laser (FEL) in the vacuum ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approximately 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width, and intensity fluctuations, are all consistent with the present models for SASE FELs.
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title: Plasma source test and simulation results for the underdense plasma lens experiment at the UCLA Neptune Laboratory
format: journal article
publisher: IEEE Transactions on Plasma Science
year: 2000
8 authors: H. Suk | C. E. Clayton | C. Joshi | T.C. Katsouleas | P. Muggli | R. Narang | C. Pellegrini | J.B. Rosenzweig
abstract: The planned plasma lens experiment at the UCLA Neptune Laboratory is described. In the experiment, electron beams with an energy of 16 MeV, a charge of 4 nC, and a pulse duration of 30 ps full-width at half-maximum (FWHM) are designed to be produced from the 1.625-cell photoinjector radio-frequency gun (f=2.856 GHz) and PWT linac in the Neptune. The generated beams are passed through a thin plasma with a density of low 10/sup 12/ cm/sup -3/ range and a thickness of a few centimeters. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. In this paper, the overview of the planned plasma lens experiment and the test results of the plasma source for various conditions are presented. In addition, computer simulations with a 2-1/2 dimensional particle-in-cell code (MAGIC) were performed and the simulation results are shown. (19 References).
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title: HOMDYN study for the LCLS RF photo-injector
format: conference proceeding
conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd
year: 2000
5 authors: M. Ferrario | Clendenin, J. E. | D. T. Palmer | J.B. Rosenzweig | L. Serafini
abstract: We report the results of a recent beam dynamics study, motivated by the need to redesign the LCLS photoinjector, that led to the discovery of a new effective working point for a split RF photoinjector. The HOMDYN code, the main simulation tool adopted in this work, is described together with its recent improvements. The new working point and its LCLS application is discussed. Validation tests of the HOMDYN model and low emittance predictions, 0.3 mm-mrad for a 1 nC flat top bunch, are performed with respect to the multi-particle tracking codes ITACA and PARMELA. (26 References).
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title: A diagnostic system to measure SASE-FEL radiation properties along the 4-meter VISA undulator
format: conference proceeding
conference: FEL 1999 21st
year: 2000
4 authors: A. Murokh | E. Johnson | J.B. Rosenzweig | A. Tremaine
abstract: During the last several years there has been a great experimental effort in the developing high gain SASE free electron lasers. Single pass FEL gain of 10 5 was achieved in the far infrared [ 1 ]. The research is directed towards smaller wavelengths and yet higher gain, with the ultimate goal of constructing the x-ray FEL [ 2 ]. A number of experiments are under the development to demonstrate SASE at visible and UV range. However, many important properties of the process of self-amplified spontaneous emission are still to be verified experimentally. As a part of the VISA experimental program (visible-to-infrared SASE amplifier [ 3 , 4 ]), we have constructed a diagnostics system, which will allow a detailed characterisation of the FEL process along the 4 meters of VISA undulator.
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title: Status and initial commissioning of a high gain 800 nm SASE FEL
format: conference proceeding
conference: FEL 1999 21st
year: 2000
22 authors: A. Tremaine | Pedro Frigola | A. Murokh | P. Musumeci | C. Pellegrini | J.B. Rosenzweig | M. Babzien | Ben-Zvi, I. | E. Johnson | R. Malone | G. Rakowsky | Skaritka, J. | X.J. Wang | Yu, L. H. | Van Bibber, K. A. | J.M. Hill | G.P. Le Sage | R. Carr | M. Cornacchia | Nuhn, H. D. | Ruland, R. | D. C. Nguyen
abstract: We describe the status and initial commissioning of the visible to infrared SASE amplifier (VISA) experiment. VISA uses a strong focusing 4 m undulator, the Brookhaven National Laboratory ATF linac with an energy of 72 MeV, and a photoinjector electron source. The VISA fundamental radiation wavelength is near 800 nm and the power expected at saturation is near 60 MW. Power, angular and spectral measurements are planned for the VISA radiation and these results will be analyzed and compared with SASE FEL theory and computer simulation. In addition, the induced electron beam micro-bunching will be measured using coherent transition radiation. (12 References).
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title: Single crystal copper photo-cathode in the BNL/SLAC/UCLA 1.6 cell RF gun
format: conference proceeding
conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd
year: 2000
3 authors: D. T. Palmer | S. Anderson | J.B. Rosenzweig
abstract: Previous experimental measurements in the two dimensional (2D) variation of the quantum efficiency, QE, of a polycrystalline copper photo-cathode have measured a 25% variation in this quantity. Two possible causes of this 2D QE variation are contamination of the photo-emitting surface and the work function variation of copper due to crystal facet orientation. We report on the progress to eliminate the 2D QE variation due to the non-uniform crystal facet orientation of copper photo-emitters. This is accomplished by replacing the polycrystalline photo-emitter region of the cathode plane in a modified version of the BNL/SLAC/UCLA 1.6 cell rf gun with a thin disk of a single crystal copper Cu_100. In this paper we present a theoretical discussion on the effect that the crystal structure orientation of a photo-emitter has on the 2D QE. The manufacturing process used in the construction of the single crystal Cu_100 photo-cathode used in these photo-emission experiments are discussed. Preliminary experimental results are presented along with a discussion of our future experimental plans.
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title: Nonequilibrium transverse motion and emittance growth in space-charge dominated beams
format: conference proceeding
conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd
year: 2000
2 authors: S. Anderson | J.B. Rosenzweig
abstract: The transverse dynamics of space-charge dominated beams are investigated both analytically and computationally, in order to understand the mechanisms for emittance oscillations and growth due to nonlinear space-charge fields. This work explores the role of space-charge dominated equilibrium and its relationship to phase space wave-breaking, which is responsible for the irreversible emittance growth in these systems. The physics of both coasting and accelerating beams are examined, in order to illuminate the most effective approaches to beam handling during the emittance compensation process, as well as during subsequent beam transport. (13 References).
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title: Plasma electron trapping and acceleration in a plasma wake field using a density transition
format: conference proceeding
conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd
year: 2000
4 authors: Suk, H. | N. Barov | J.B. Rosenzweig | E. Esarey
abstract: A new scheme for plasma electron injection into an acceleration phase of a plasma wake field is presented. In this scheme, a short single electron beam bunch is sent through an underdense plasma with a sharp downward density transition and some plasma electrons are trapped in the plasma wake field due to the rapid wavelength increase of the wake wave at the density transition. To investigate the trapping and acceleration mechanism, two-dimensional particle-in-cell (PIC) simulations were performed, and the illustrative 2-D simulation shows that the new injection method can produce a relatively large charge (~0.5 nC), short (~1 ps) and high energy (> driving beam energy) electron beam pulse with a plasma density transition from 5x10(13) cm(-3) to 3.5x10(13) cm(-3). In addition to the 2-D simulations, 1-D analytic work based on the Hamiltonian formalism and 1D simulations have been performed and the results are also presented. Finally, a proposed experiment at the Neptune Laboratory of UCLA is described.
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title: Limitations on the resolution of YAG:Ce beam profile monitor for high brightness electron beam
format: conference proceeding
conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd
year: 2000
5 authors: A. Murokh | V. Yakimenko | E. Johnson | X.J. Wang | J.B. Rosenzweig
abstract: The performance of single crystal YAG:Ce (Y_(3)Al_(5)O_(12)) beam profile monitors was studied for transverse masurements on the high brightness ultrarelativistic electron beam at Accelerator Test Facility (ATF) at BNL. The test demonstrated systematic intensity dependent beam enlargement on YAG monitors, compared to other diagnostics. Possible mechanisms of the effect have been studied. The quantitative examination was performed and compared to the developed phenomenological models. Limitations on the use of YAG:Ce diagnostics are discussed with respect to the high-brightness electron sources.
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title: The development of S-band plane wave transformer photoinjector
format: conference proceeding
conference: PAC 1999
year: 1999
11 authors: X. Ding | C. Pellegrini | J.B. Rosenzweig | S. Telfer | A. Tremaine | Vernon, W. | D. Yu | D. Newsham | Zeng, J. | Lee, T. | Chen, J.
abstract: An integrated S-band RF photoinjector based on the plane wave transformer (PWT) is being built in the Particle Beam Physics Laboratory at UCLA in collaboration with DULY Research. This novel structure integrates a photocathode directly into a PWT linac making the structure simple and compact. Due to the strong coupling between each adjacent cell, this structure is relatively easy to fabricate and operate. This photoinjector can provide high brightness beams at energies of 15 to 20 MeV, with emittance less than 1 mm-mrad at charge of 1 nC. These short-pulse beams can be used in various applications: space charge dominated beam physics studies, plasma lenses, plasma accelerators, free-electron laser microbunching techniques, and SASEFEL physics studies. It will also provide commercial opportunities in chemistry, biology and medicine. The present status of the PWT photoinjector including fabrication and cold test to characterise the structure is described. RF system and photocathode drive laser system are also discussed.
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title: A measurement of high gain SASE FEL induced electron beam micro-bunching using coherent transition radiation
format: conference proceeding
conference: PAC 1999
year: 1999
9 authors: A. Tremaine | S. Anderson | Pedro Frigola | M. Hogan | A. Murokh | C. Pellegrini | J.B. Rosenzweig | D. C. Nguyen | Sheffield, R.
abstract: Coherent transition radiation (CTR) was used to study the longitudinal modulations of an electron beam exiting the UCLA/LANL high gain SASE FEL. The induced longitudinal micro-bunching of the electron beam at the exit of the undulator was measured with a frequency domain technique using the CTR emitted when this beam strikes a thin conducting foil. Formalisms for both CTR and SASE theories are related using the simulation code GINGER in which the SASE FEL gain of the output radiation and the micro-bunching of the electron beam are given. Experimental results from the CTR measurement will show the limit of standard transition radiation theory is being approached and new analysis is needed. (8 References).
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title: Commissioning of the Neptune photoinjector
format: conference proceeding
conference: PAC 1999
year: 1999
21 authors: S. Boucher | P. Musumeci | Loh, M. | Burke, A. | S. Anderson | J.B. Rosenzweig | K. Bishofberger | X. Ding | Holden, T. | A. Murokh | C. Pellegrini | Suk, H. | A. Tremaine | C. Clayton | C. Joshi | Marsh, K. | P. Muggli | M.C. Thompson | S. Anderson | R. Agustsson | R. J. England
abstract: The status of the commissioning of the RF photoinjector in the Neptune advanced accelerator laboratory is discussed. The component parts of the photoinjector, the RF gun, photocathode drive laser system, booster linac, RF system, chicane compressor, beam diagnostics systems, and control system are described. This injector is designed to produce short pulse length, high brightness electron beams. Experiments planned for the immediate future are described. Initial measurements of various beam parameters are presented. (10 References).
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title: First results of the Fermilab high-brightness RF photoinjector
format: conference proceeding
conference: PAC 1999
year: 1999
18 authors: J.P. Carneiro | R.A. Carrigan | Champion, M. S. | P. L. Colestock | H. T. Edwards | Fuerst, J. D. | W. H. Hartung | Koepke, K. P. | Kuchnir, M. | J. K. Santucci | Spentzouris, L. K. | Fitch, M. J. | Melissinos, A. C. | P. Michelato | C. Pagani | Sertore, D. | N. Barov | J.B. Rosenzweig
abstract: A collaboration has been formed between FNAL, UCLA, LNFN Milano, the University of Rochester, and DESY to develop the technology of an RF photoinjector, followed by a superconducting cavity, to produce high bunch charge (8 nC) with low normalized emittance ([left angle bracket]20 mm mrad) in bunch spacing trains of 800 bunches separated by mu s. The activities of bunch charge the collaboration fall into two categories: 1. the development of Injector II for the TeSLA/TTF accelerator. This photoinjector (TTF RF Gun) was tested at Fermilab in September and October 1998 and installed at DESY in November 1998. 2. the installation at the A0 Hall of Fermilab of a modified version of the TTF photoinjector, for photoinjector R&D and to study novel applications of high-brightness, pulsed electron beams. This photoinjector (A0 RF Gun) produced its first beam in March 1999. This paper presents a summary of the tests done at Fermilab on the TITF Injector II and the first results obtained on the new Fermilab photoinjector.
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title: Optimal scaled photoinjector designs for FEL applications
format: conference proceeding
conference: PAC 1999
year: 1999
5 authors: J.B. Rosenzweig | S. Anderson | X. Ding | C. Pellegrini | G. Travish
abstract: Much of the research and development surrounding the effort to create X-ray FELs based on the SASE process has centered on the creation of ultra-high brightness electron beam sources. The sources for existing short wavelength FEL designs, which employ RF photoinjector technology, have all been specified to contain 1 nC of charge. We show, by scaling existing designs, that this constraint causes the maximum beam brightness to be found when the RF wavelength is shortened to X-band. If, instead of holding the charge constant, we assume a certain RF wavelength device and then scale the charge, notable improvements in the beam brightness, and thus the FEL performance, are found. Charge scaling assumes that the density and aspect ratio of the beam stays constant as the charge is changed. If we relax the requirement of a constant aspect ratio in order to maximize the beam current and brightness by shortening the beam pulse, we find that the pulse lengthening due to space charge eventually brings this effort to a stop. The results of this investigation and their impact on SASE FEL design is discussed.
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title: A Comparison Between the Performance of Split and Integrated RF Photoinjectors
format: conference proceeding
conference: PAC 1999
year: 1999
4 authors: J.B. Rosenzweig | S. Anderson | X. Ding | L. Serafini
abstract: RF photoinjectors, the present source of choice for production of ultra-high brightness electron beams, have two basic design types: split, in which a short, high gradient rf gun is followed by a a drift and a booster linac, and a lower gradient integrated photoinjector, in which the linac acceleration is connected directly to the gun. The first type is represented at UCLA by the Neptune photoinjector, the second by the newly constructed S-band PWT photoinjector. We examine, through simulation and theory, the relative merits of each type of injector, both from the point of view of the beam physics (ability of the source to produce high currents and low emittances), and of relative technical advantages.
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title: Slab symmetric dielectric micron scale structures for high gradient electron acceleration
format: conference proceeding
conference: PAC 1999
year: 1999
2 authors: P.V. Schoessow | J.B. Rosenzweig
abstract: A class of planar microstructures is proposed which provide high accelerating gradients when excited by an infrared laser pulse. These structures consist of parallel dielectric slabs separated by a vacuum gap; the dielectric or the outer surface coating are spatially modulated at the laser wavelength along the beam direction so as to support a standing wave accelerating field. We have developed numerical and analytic models of the accelerating mode fields in the structure. We show an optimized coupling scheme such that this mode is excited resonantly with a large quality factor. The status of planned experiments on fabricating and measuring these planar structures is described. (9 References).
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title: Photon beam diagnostics for VISA FEL
format: conference proceeding
conference: PAC 1999
year: 1999
17 authors: A. Murokh | C. Pellegrini | J.B. Rosenzweig | Pedro Frigola | P. Musumeci | A. Tremaine | M. Babzien | Ben-Zvi, I. | A. Doyuran | E. Johnson | Skaritka, J. | X.J. Wang | Van Bibber, K. A. | J.M. Hill | G.P. Le Sage | D. C. Nguyen | M. Cornacchia
abstract: The VISA (Visible to Infrared SASE Amplifier) project is designed to be a SASE-FEL driven to saturation in the sub-micron wavelength region. Its goal is to test various aspects of the existing theory of self-amplified spontaneous emission, as well as numerical codes. Measurements include: angular and spectral distribution of the FEL light at the exit and inside of the undulator; electron beam micro-bunching using CTR; single-shot time resolved measurements of the pulse profile, using an auto-correlation technique and FROG algorithm. The diagnostics are designed to provide maximum information on the physics of the SASE-FEL process, to ensure a close comparison of the experimental results with theory and simulations. (9 References).
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title: A permanent-magnet focused X-band photoinjector
format: conference proceeding
conference: PAC 1999
year: 1999
8 authors: D. Yu | D. Newsham | Wilson, P. | Zeng, J. | J.B. Rosenzweig | X. Ding | F. Hartemann | Landahl, E.
abstract: A Plane-Wave-Transformer (PWT), integrated photoinjector operating at an X-band frequency (8.547GHz) is being developed by DULY Research Inc. in a DOE SBIR project, in collaboration with UCLA and UCD/ILSA. Upward frequency scaling from an S-band PWT photoinjector would result in a compact photoinjector with unprecedented brightness. Challenging technological innovations are required at X-band. In particular, water cooling capacity, mechanical support strength, and materials properties do not scale linearly with frequency. Instead of using large solenoids, we have successfully designed the required focusing for an X-band PWT using a compact, permanent magnet system. Also described in this paper is a system design of the X-band photoinjector, including the RF system and the cooling/support of the PWT structure.
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title: Output power control in an X-ray FEL
format: conference proceeding
conference: PAC 1999
year: 1999
3 authors: C. Pellegrini | X. Ding | J.B. Rosenzweig
abstract: Recent theoretical and experimental advances of the high gain self-amplified spontaneous emission free-electron laser (SASE-FEL), have demonstrated the feasibility of using this system as a 4/sup th/ generation light source. This source will produce diffraction-limited radiation in the 0.1 nm region of the spectrum, with peak power of tens of GW, subpicosecond pulse length, and very large brightness. The peak power density in such a system is very large, and in some experiments it might damage the optical systems or the samples, or it might be simply larger than what is needed for the particular experiment being considered. Some options to reduce the power level, for example by using a gas absorption cell to reduce the X-ray intensity, have been studied. In this paper we discuss another possibility to control the power output of an X-ray SASE-FEL by varying the charge from the electron source, and the longitudinal bunch compression during the acceleration in the linac.
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title: Underdense plasma lens experiment at the UCLA Neptune Laboratory
format: conference proceeding
conference: PAC 1999
year: 1999
10 authors: Suk, H. | C. E. Clayton | G. Hairapetian | C. Joshi | Loh, M. | P. Muggli | R. Narang | C. Pellegrini | J.B. Rosenzweig | T.C. Katsouleas
abstract: An underdense plasma-lens experiment is planned at the UCLA Neptune Laboratory. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. Test results of the plasma source show that it can provide satisfactory Ar plasma parameters for underdense plasma lens experiments, i.e., a density in the low 10/sup 12/ cm/sup -3/ range and a thickness of a few cm. In the plasma chamber a YAG slab and a Cherenkov radiator are placed for electron beam diagnostics so that both time-integrated and time-resolved information will be obtained and compared with the MAGIC code (2 and 1/2 dimensional particle-in-cell) simulations. In this paper, the planned experiment including test results of the plasma source, diagnostics and MAGIC simulation results is presented. (5 References).
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title: The effects of RF asymmetries on photoinjection beam quality
format: conference proceeding
conference: PAC 1999
year: 1999
4 authors: J.B. Rosenzweig | S. Anderson | X. Ding | D. Yu
abstract: A general multipole-based formalism to study the effects of RF asymmetries on the production of ultra-high brightness beam is presented, which employs both analytical and computational techniques. These field asymmetries can cause the degradation of beam emittance due to time dependent and nonlinear focusing effects. Two cases of interest are examined: the dipole asymmetry produced by a coupling slot in a standard high gradient RF gun, and the higher multipole content introduced by the support/cooling rods in a PWT structure. Practical implications of our results, as well as comparison to cold test and beam-based experimental tests, are discussed. (8 References).
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title: Ultrafast X-ray generation and applications using laser-linac interactions
format: conference proceeding
conference: IEEE LEOS Annual Meeting 1999
year: 1999
9 authors: T. Ditmire | T. E. Cowan | G. LeSage | M. Allen | G. Hays | K. B. Wharton | M. D. Perry | H. T. Powell | J.B. Rosenzweig
abstract: At LLNL we have been working to integrate an intense short-pulse laser with a low-emittance relativistic electron beam utilizing a 100 MeV S-band linac. This project uses a 100 TW, 35 fs laser, which is currently under development. (3 References).
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title: Measured free-electron laser microbunching using coherent transition radiation
format: conference proceeding
conference: FEL 1998 20th
year: 1999
9 authors: A. Tremaine | J.B. Rosenzweig | S. Anderson | Pedro Frigola | M. Hogan | A. Murokh | C. Pellegrini | D. C. Nguyen | Sheffield, R.
abstract: The microbunch distribution of an electron beam exiting a SASE free-electron laser has been measured using the emitted coherent transition radiation (CTR) produced from a thin aluminum foil placed at the end of the undulator. The wavelength of the coherent transition radiation is shown to be the same as the FEL wavelength, and thus a measure of the beam microbunch spacing. Also, the study of the CTR linewidth and angular acceptance of the radiation captured are shown to be derived from this coherent radiative process. Scattering effects on the forward emitted transition radiation from the electron beam traversing an aluminum foil are also considered. (11 References).
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title: An Optimized Slab-Symmetric Dielectric-Based Laser Accelerator Structure
format: conference proceeding
conference: AAC 1998 8th
year: 1999
2 authors: J.B. Rosenzweig | Schoessow, P.
abstract: A slab-symmetric, partially dielectric filled, laser excited structure which may be used to accelerate charged particles is analyzed theoretically and computationally. The fields associated with the accelerating mode are calculated, as are aspects of the resonant filling and impedance matching of the structure to the exciting laser. It is shown through computer simulation that the accelerating mode in this structure can be excited resonantly and with large quality factor Q. Practical aspects of implementing this structure as an accelerator are discussed. (7 References).
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title: Synchronization of sub-picosecond electron and laser pulses
format: conference proceeding
conference: AAC 1998 8th
year: 1999
2 authors: J.B. Rosenzweig | G.P. Le Sage
abstract: Pulse-compression techniques apply a longitudinal restoring force which improves synchronization between electron bunches and the RF drive, partially or completely correcting errors in the exit time from the injector. While this feature is beneficial in terms of linac related phase matching issues and jitter in the photocathode laser system, laser jitter with respect to the RF clock is in fact worsened in terms of the final interaction of laser and electron pulses. That is, if one attempts to synchronize the electron bunch to an external laser, deriving external laser timing from, say, the photocathode drive laser oscillator, the relative timing of electron and the external laser will be mismatched, because the electron beam is pulled toward a given phase of the RF clock. Thus, if one wishes to take advantage of the locking of the electron beam to the (assumed stable) RF clock, then an equivalent mechanism must be found for locking the external laser to the RF clock as well.
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title: The design for the LCLS RF photoinjector
format: conference proceeding
conference: FEL 1998 20th
year: 1999
16 authors: R. Alley | Bharadwaj, V. | Clendenin, J. E. | P. Emma | Fisher, A. | Frisch, J. | Kotseroglou, T. | R. H. Miller | D. T. Palmer | Schmerge, J. F. | Sheppard, J. C. | Woodley, M. | Yeremian, A. D. | J.B. Rosenzweig | D. Meyerhofer | L. Serafini
abstract: We report on the design of the RF photoinjector of the Linac Coherent Light Source. The RF photoinjector is required to produce a single 150 MeV bunch of similar to 1 nC and similar to 100 A peak current at a repetition rate of 120 Hz with a normalized rms transverse emittance of similar to 1 pi mm-mrad. The design employs a 1.6-cell S-band RF gun with an optical spot size at the cathode of a radius of similar to 1 mm and a pulse duration with an rms sigma of similar to 3 ps. The peak RF field at the cathode is 150 MV/m with extraction 57 degrees ahead of the RF peak. A solenoidal field near the cathode allows the compensation of the initial emittance growth by the end of the injection linac. Spatial and temporal shaping of the laser pulse striking the cathode will reduce the compensated emittance even further. Also, to minimize the contribution of the thermal emittance from the cathode surface, while at the same time optimizing the quantum efficiency, the laser wavelength for a Cu cathode should be tunable around 260 nm. Following the injection linac the geometric emittance simply damps linearly with energy growth. PARMELA simulations show that this design will produce the desired normalized emittance, which is about a factor of two lower than has been achieved to date in other systems. In addition to low emittance, we also aim for laser amplitude stability of 1% in the UV and a timing jitter in the electron beam of 0.5 ps rms, which will lead to less than 10% beam intensity fluctuation after the electron bunch is compressed in the main linac.
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title: Test results of the plasma source for underdense plasma lens experiments at the UCLA Neptune Lab
format: conference proceeding
conference: AAC 1998 8th
year: 1999
7 authors: Suk, H. | C. E. Clayton | R. Narang | P. Muggli | J.B. Rosenzweig | C. Pellegrini | C. Joshi
abstract: A plasma source was developed at UCLA for planned underdense plasma lens experiments, where the plasma density is less than the electron beam density. The argon plasma, produced by a discharge between a LaB_6 cathode at 1330 degrees C and a tantalum anode, is confined by a solenoidal magnetic field and flows transversely across the electron beam path. Extensive test of the plasma source is under way for various conditions before it is assembled with the UCLA photocathode-based electron linac. In particular, different longitudinal (with respect to the electron beam) plasma profiles and effective plasma lengths can be obtained by adjusting the moveable sliding door between the plasma source and the transverse beamline. Test results of the plasma source are presented. (11 References).
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title: Coherent transition radiation-based diagnosis of electron beam pulse shape
format: conference proceeding
conference: AAC 1998 8th
year: 1999
3 authors: J.B. Rosenzweig | A. Murokh | A. Tremaine
abstract: The bunch shapes of an electron beams is increasingly difficult to measure, as the time-scales of interest are now sub-picosecond. We discuss here the use of coherent transition radiation (CTR) for such measurements. Two types of measurements are presented: the deduction of macroscopic (0.3 psec resolution) pulse profile using interferometry, and the examination of microbunch (50 fsec) structure from an FEL-bunched beam using spectral characteristics of the CTR. For the macrobunch measurement we discuss the problem of missing low frequency radiation and one solution for extracting meaningful data with this problem are presented. For microbunch CTR, we examining initial spectrally-resolved measurements, and some interesting deviations in the CTR spectrum from the standard theoretical predictions. (23 References).
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title: The VISA FEL Undulator
format: conference proceeding
conference: FEL 1998 20th
year: 1999
14 authors: R. Carr | I. Ben-Zvi | L. Bertolini | M. Cornacchia | P. Emma | Pedro Frigola | E. Johnson | M. Libkind | S. Lidia | H. D. Nuhn | C. Pellegrini | G. Rakowsky | J.B. Rosenzweig | R. Ruland
abstract: The Visible-Infrared SASE Amplifier (VISA) FEL is an experimental device designed to show self amplified spontaneous emission (SASE) to saturation in the 800-600 nm range, where silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is the first SASE FEL designed to saturate, and its diagnostics will provide important checks of theory.
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title: Measurements of gain larger than 10(5) at 12 mu m in a self-amplified spontaneous-emission free-electron laser
format: journal article
publisher: Physical Review Letters
year: 1998
13 authors: M. Hogan | C. Pellegrini | J.B. Rosenzweig | S. Anderson | Pedro Frigola | A. Tremaine | C. Fortgang | D. C. Nguyen | R. L. Sheffield | J. Kinross-Wright | A. A. Varfolomeev | S. Tolmachev | R. Carr
abstract: We report measurements of very large output intensities corresponding to a gain larger than 10/sup 5/ for a single pass free-electron laser operating in the self-amplified spontaneous emission (SASE) mode at 12 mu m. We also report the observation and analysis of intensity fluctuations of the SASE radiation intensity in the high-gain regime. The results are compared with theoretical predictions and simulations. (18 References).
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title: Beam transport, acceleration and compression studies in the Fermilab high-brightness photoinjector
format: conference proceeding
conference: Linear Accelerator Conference 1998
year: 1998
20 authors: J.P. Carneiro | R. Carrigan | Champion, M. S. | A. Cianchi | E.R. Colby | P. L. Colestock | H. T. Edwards | Fuerst, J. D. | W. Hartung | Koepke, K. P. | Kuchnir, M. | Spentzouris, L. K. | Fitch, M. J. | Fry, A. R. | Melissinos, A. C. | Taylor, B. D. | P. Michelato | Sertore, D. | C. Pagani | J.B. Rosenzweig
abstract: A photoinjector is being constructed in order to produce a pulse train of up to 800 electron bunches, each with 8 nC of charge and a 3.5 ps rms bunch length. The spacing between bunches within a train is 1 s and the train repetition rate is 1?10 Hz. The desired transverse emittance is <20 mm mrad. An rf photo-gun delivers a bunched 4?5 MeV beam which will be accelerated to 14?18 MeV by a 9- cell superconducting cavity and compressed magnetically. Measurements have been done on the beam delivered by a first prototype rf gun; installation of a new rf gun, the 9-cell cavity, and the bunch compressor is in progress.
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title: High brightness electron sources
format: conference proceeding
conference: Linear Accelerator Conference 1998
year: 1998
1 author: J.B. Rosenzweig
abstract: The production of unprecedentedly high brightness electron beams is a critical aspect of many applications, from free-electron lasers to advanced accelerators. The preferred method for obtaining these beams is the radiofrequency photoinjector. The physics and technology aspects of this device are reviewed here, along prospects for future progress in high-brightness beam development.
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title: Laminar flow in non-relativistic intense proton beams
format: conference proceeding
conference: EPAC 1998
year: 1998
2 authors: L. Serafini | J.B. Rosenzweig
abstract: An approach to the envelope description of laminar non-relativistic particle beams is presented, which describes a new kind of equilibrium flow for strongly space charge dominated proton beams subject to acceleration in RF Linacs. The analysis is based on the extension of the invariant envelope concept, recently introduced in the field of RF photo-injectors[1], to nonrelativistic particle beams whose envelope is dominated by coherent plasma oscillations instead of incoherent betatron motion associated to thermal rms emittance. An exact analytical solution of the rms envelope equation is presented, describing both the laminar regime and the transition to the thermal regime: the impact of this new beam equilibrium on the design of high intensity Linacs is discussed.
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title: Measurements of High Gain and Intensity Fluctuations in a Self-Amplified, Spontaneous-Emission Free-Electron Laser
format: journal article
publisher: Physical Review Letters
year: 1998
12 authors: M. Hogan | C. Pellegrini | J.B. Rosenzweig | G. Travish | A. A. Varfolomeev | S. Anderson | K. Bishofberger | Pedro Frigola | A. Murokh | N. Osmanov | Sven Reiche | A. Tremaine
abstract: We report measurements of large gain for a single pass free-electron laser operating in self-amplified spontaneous emission (SASE) at 16 mm starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high gain regime. The results are compared with theoretical predictions and simulations.
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title: Analysis of the Evolution of Classical Distribution Functions Using Quantum Methods
format: conference proceeding
conference:
year: 1998
1 author: J.B. Rosenzweig
abstract:
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title: Diamagnetic fields due to finite-dimension intense beams in high-gain free-electron lasers
format: journal article
publisher: Physical Review E
year: 1998
2 authors: J.B. Rosenzweig | P. Musumeci
abstract: High-gain, self-amplified spontaneous emission free-electron lasers (SASE FEL's), with proposed operation in wavelengths extending down to X-rays, require intense relativistic electron beams, which under certain conditions can generate large diamagnetic fields. The action of these fields has the potential to seriously degrade FEL performance. It is shown here by both analysis and simulation that the finite size of the electron beams diminishes this effect so that it is negligible for proposed SASE FEL's. . (12 References).
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title: First observation of luminosity-driven extraction using channeling with a bent crystal
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 1998
26 authors: R. Carrigan | D. Chen | G. Jackson | N. Mokhov | C.T. Murphy | S. I. Baker | S. A. Bogacz | D. B. Cline | S. Ramachandran | J. Rhoades | J.B. Rosenzweig | A. Asseev | R. A. Biryukov | A. Taratin | J. A. Ellison | A. Khanzadeev | T. Prokofieva | V. Samsonov | G. Solodov | B. Newberger | E. Tsyganov | H. J. Shih | W. Gabella | B. Cox | V. Golovatyuk | A. McManus
abstract: Luminosity-driven channeling extraction has been observed for the first time using a 900 GeV circulating proton beam at the superconducting Fermilab Tevatron. The extraction efficiency was found to be about 30%. A 150 kHz beam was obtained during luminosity-driven extraction with a tolerable background rate at the collider experiments. A 900 kHz beam was obtained when the background limits were doubled. This is the highest energy at which channeling has been observed.
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title: Observation of Self-Amplified Spontaneous-Emission-Induced Electron-Beam Microbunching Using Coherent Transition Radiation
format: journal article
publisher: Physical Review Letters
year: 1998
9 authors: A. Tremaine | J.B. Rosenzweig | S. Anderson | Pedro Frigola | M. Hogan | A. Murokh | C. Pellegrini | D. C. Nguyen | R. L. Sheffield
abstract: We report the measurement of electron-beam microbunching at the exit of a self-amplified spontaneous-emission free-electron laser (SASE FEL), by observation of coherent transition radiation (CTR). The CTR was found to have an angular spectrum much narrower than spontaneous transition radiation and a narrow-band frequency spectrum. The central frequency of the fundamental CTR spectrum is found to differ slightly from that of the SASE, a finding in disagreement with previously invoked CTR theory. The CTR measurement establishes the uniformity of microbunching in the transverse dimension, indicating the SASE FEL operates in a dominant transverse mode.
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