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73 preprints:

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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: Status of UCLA IR FEL
format: preprint
year: 1996
21 authors: C. Pellegrini | G. Baranov | N. Barov | P. Davis | M. Fauver | B. Gitter | G. Hairapetian | S. Hartman | M. Hogan | S. Ivanchenkov | C. Joshi | A. Khlebnikov | P. Kwok | N. Luhmann | S. Park | J.B. Rosenzweig | K. Schenk | Smolin, J. A. | P. Tran | G. Travish | A. A. Varfolomeev
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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: 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
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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
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title: Short Pulse and Diagnostic Beamline Characteristics
format: preprint
year: April 10, 1991
1 author: J.B. Rosenzweig
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title: Degradation of Longitudinal Phase Space Distribution of the LCLS Beam by Compton Back-Scattering
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year: January 24, 1993
1 author: J.B. Rosenzweig
abstract: The requirements on the phase and amplitude jitter of the photoinjector laser in teh LCLS are very stringent. These can be eased if the incoherent energy spread in the beam is increased, decreasing the sensitivity of the bunch compression process. There are few good ways of increasing the incoherent, as opposed to the coherent, energy spread, which can be easily increased by rephasing the rf, or by space charge. A radiative or a collisional process must be used to increase the incoherent energy spread, in order to make the energy change independent of phase. Here we examine the feasibility of using the back-scattering of photons from an intense, one picosecond laser beam. We assume that we can use a laser beam (1047 nm wavelength, Nd:YLF), chosen to allow it to drive both the cathode (after quadrupling), and the longitudinal phase space degrader.
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title: The Photocathode Gun: Shunt Impedance and Field Balance
format: preprint
year: April 26, 1993
1 author: J.B. Rosenzweig
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title: Redesign of the Low Energy Beam Transport in the UCLA Photoinjector
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year: June 24, 1993
1 author: J.B. Rosenzweig
abstract: The low energy transport of the beam in teh UCLA photoinector has been the source of experimental difficulties associated with preserving the emittance and the pulse length while the beam experience large self-forces due to space charge. While some of the difficulties (most notably the pulse lengthening) can be mitigated by previous experiments, a major improvement should result from minimixing the low energy beam transport region from teh gun to the linac.
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title: RF Photoinjectors: A Guide to Performance Requirements and Demands on Laser Systems
format: preprint
year: 1994
1 author: J.B. Rosenzweig
abstract: This paper describes the demands on drive laser performance made by the performance expected of present and future rf photocathode injectors. We review the relevant charged particle beam physics of rf photocathode guns as well as the technology and physics applications of these devices. The role of the drive laser is examined within this context. Several examples of demanding future rf photoinjector systems are discussed.
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title: Report of the Working Group on Electron Sources
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year: 1994
2 authors: J.B. Rosenzweig | J.B. Rosenzweig
abstract: We report in this paper on the activities of the working group on electron sources at the Advanced Accelerator Workshop held in Lake Geneva, Wisconsin in June 1994. The discussion, while dominated by the subject of rf photoinjectors, included explorations of many novel areas in the state-of-the-art in electron source reserach and development. The major points raised at the workshop are examined, and a guide to the detailed reports of the members of the working group is provided.
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title: The SATURNUS Modulator
format: preprint
year: 1991
1 author: Terrien, C.
abstract: A Free Electron Laser operating in the infrared region is under contstruction at UCLA. It will be driven by a compact 20 MeV linac, and a high brightness RF electron gun will be used as the injector.
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title: Development of a Compact Focusing Solenoid for Photocathode Guns
format: preprint
year: 1993
1 author: M.C. Thompson
abstract: A compact solenoid is being developed for the purpose of focusing an electron beam exiting a RF/photocathode electron gun. The size and power consumption of the solenoids in place make a smaller, more efficient solenoid desirable. The present state of this design is shown, including the physical appearance and field profile.
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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: SATURNUS Quadrupole Magnet Field Preliminary Measurements
format: preprint
year: 1992
2 authors: P. Tran | G. Travish
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title: Comparison of the FEL and CSR Instabilities
format: preprint
year: April 19, 2002
1 author: Sven Reiche
abstract: FEL and CSR instabilities have same principle of interaction between electron beam and synchrotron radiation, but the signature is different for the different longitudinal scales. Beside the FEL these instabilities are regarded as degrading affects on the beam properties, imposing limitation on the operation range of the accelerator.
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title: Pulsed Wire Measurements of the UCLA/Kurchatov Undulator at LANL
format: preprint
year: 1993
1 author: G. Travish
abstract: An undulator magnet designed and built by the Kurchatov Institute in Russia for the UCLA FEL program has been characterized using the pulsed wire method at the Los Alamos National laboratory (LANL). The pulsed wire is better suited to measuring off axis fields than the previously employed Hall probes. The speed and simplicity of the pulsed wire measurements also affords more rapid tuing and correction of undulators. Results from both methods are presented here and shown to compare favorably. The on axis second integral of the undulator field is found to be uniform. There are entrance quadrupole as well as entrance dipole fields in the undulator; however, as is discussed in the paper, these fields do not present a problem. There is also a quadrupole component throughout the undulator. Further numerical analysis of the data is required, but the magnitude appears to be small. The experimental arrangement used is described in detail in the hopes of implementing such a system at UCLA.
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title: Some Performance Parameters and Figures of Merit for Photoinjector Drive Lasers
format: preprint
year: 2002
1 author: G. Travish
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title: Free-Electron Simulations at Short Wavelengths
format: preprint
year: May 01, 2002
1 author: Sven Reiche
abstract: Outline: FEL Simulations Overview Codes Shot-Noise Models Short Wavelength Effects Spontaneous Radiation Wake Fields Undulator Description Start-End Simulations
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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
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title: Velocity Bunching: ORION, PLEIADES and NEPTUNE
format: preprint
year: May 3, 2002
1 author: J.B. Rosenzweig
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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: 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: Modeling Photo-desorption in High Current Storage Rings
format: preprint
year: 1991
1 author: W. Barletta
abstract: A phenomenological model of photo-desorption that includes effects of dose dependence and diffuse photon reflection allows one to compute the leveling of gas loads high current storage rings that typify heavy flavor factories. The model also permits one to estimate chamber commissioning times.
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title: 3.5 Cell R.F. Gun Simulation with Spacecharge and Focusing Coil U.C.L.A. IRFEL Note H.1
format: preprint
year: November 9, 1989
1 author: S. Hartman
abstract: Using the particle simulation code PARMELA, I calculated the emittance values for a three and one half cell gun. Since the beam suffers a R.F. defocusing at the exit of the last cell a solenoidal focusing element was added to cancel the divergence effect.
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title: Design of the Vacuum System for the High Energy Ring of an Asymmetric B-Factory Based on PEP
format: preprint
year: 1991
4 authors: W. Barletta | M. Calderon | R. Wong | T. Jenkins
abstract: The multi-ampere currents required for high luminosity operation of an asymmetric B factory leads to extremely stressing requirements on a vacuum system suitable for maintaining long beam-gas lifetimes and acceptable background levels in the dtector. We present the design for a Cu alloy vacuum chamber and its associated pumping system for the 9GeV electron storage ring of the proposed B factory based on PEP. The excellent thermal and photo-desorption properties of Cu allows handling the high photon flux in a conventional, single chamber design with distributed ion pumps. The x-ray opacity of the Cu is sufficiently high that no additional lead shielding is necessary to protect the dipoles from the intense synchrotron radtiation generated by the beam. The design allows chamber commissioning in <500 hr of operation.
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title: Vacuum Design for a Superconducting Mini-collider
format: preprint
year: 1991
2 authors: W. Barletta | S. Monteiro
abstract: The phi factory (Superconducting Mini-Collider or SMAC) proposed for construction at UCLA is a single storage rign with circulating currents of 2A each of electrons and positrons. The small circumference exacerbates the difficulties of handling the gas load due to photo-desorption from the chamber walls. We analyze the vacuum system for the phi factory to specify design choices.
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title: Cold Test Measurements of the UCLA Photo-Injector
format: preprint
year: April 30, 1993
2 authors: S. Hartman | M. Hogan
abstract:
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title: Quadrupole Magnets Measurement
format: preprint
year: 1992
3 authors: N. Barov | Tran, P. | M.C. Thompson
abstract: Field measurement as a function of position and current of the SATURNUS compact accelerator's quadrupole magnets was carried out using a Hall probe mounted on a simple carriage setup consisting of 3 precision linear translators and a 360-degree rotator. From this measurement, the displacement of the magnetic center from the geometric center and the effective length of each quadrupole were calculated. Also, changes in the measured magnetic field of one quadrupole due to the effect of its disassembly and reassembling were investigated. The results are reported in this paper.
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title: Measurement of the Dipole Magnets
format: preprint
year: 1993
4 authors: N. Barov | Tran, P. | M.C. Thompson | B. Gitter
abstract: The four Saturnus dipole magnets were calibrated with a Hall probe using a machinist's rotary table and a stepping motor to vary position. The setup was controlled by a Macintosh LC computer using LabView software. The field vs. current relationship was also measured. Single particle motion through the magnet was simulated, making a comparison of the real magnet to an ideal one.
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title: High Brightness Symmetric Emittance RF Photoinjector Preliminary Design Report
format: preprint
year: September 15, 1994
3 authors: E. Colby | J. F. Ostiguy | J.B. Rosenzweig
abstract: A preliminary design for a high bunch charge (8 nC), low emittance (> 20 mm-mr) radiofrequency electron photoinjector matched to the requirements of the Tesla Test Facility is presented. A 1.5 cell iris coupled pi-mode structure with high average accelerating gradient is chosen for its high shunt impedance, simplicity, and ability to accommodate an externally mounted solenoid for simultaneous beam divergence control an demittance compensation. Beam optics are optimized for an overall injector consisting of the electron gun followed by one linac capture section, a dipole chicane for magnetic bunch compression to achieve a bunch length corresponding to sigma_z = 1 mm. Electrical and beam dynamical aspects of the photoinjector design are presented. A description of the proposed experimental program is included.
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title: 25 MeV Injector for the Plasma Beat Wave Accelerator
format: preprint
year: 1994
5 authors: C. Joshi | M. Lampel | S. Park | C. Pellegrini | R. Zhang
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title: Focusing of a Relativistic Electron Beam by an Underdense Plasma Lens
format: preprint
year: 1994
5 authors: P. Davis | G. Hairapetian | C. Clayton | C. Joshi | C. Pellegrini
abstract: Plasma Lenses produce focusing gradients exceeding those of conventional quadrupole magnets by several orders of magnitude. We have recently observed dynamic focusing by an overdense plasma lens [G. Hairapetian, et al., Phys.Rev.Lett. 72, 2403 (1994)]. Theoretically, an underdense plasma lens could offer several advantages over the overdense lens: ...
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title: Modeling of the X-ray Radiation Dependence on Power in High Gradient Radio-frequency Accelerator Structures
format: preprint
year: October 9, 1995
2 authors: D. Gooden | J.B. Rosenzweig
abstract: It has long been known that field-emitted (FE) electron current is what generates the x-ray radiation from high-power RF accelerating strucutures, but it has not yet been qualitatively understood how the radiation varies with the microwave power input to these structures. This paper will show that from successive measurements of the RF power at a single position and the corresponding radiation dose rate ...
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title: 1.5 Cell R.F. Gun Simulation with coil and Space Charge U.C.L.A. IRFEL Note H.3
format: preprint
year: January 9, 1990
1 author: S. Hartman
abstract: Simulations were done to explore the effect of placing a coil along the beamline to minimize the divergent lense effect of the exit of the last cell of the gun....etc.
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title: PARMELA simulation of the U.C.L.A. compact linac
format: preprint
year: February 11, 1991
1 author: S. Hartman
abstract: The compact laser-driven R.F. linac for the SATURNUS project has been modeled using the particle dynamics simulation code PARMELA....etc.
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title: Photocathode Emission: The effects of high bandwidth drive lasers on thermal emittance
format: preprint
year: 2003
1 author: G. Travish
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title: Memo: RF Power for the PWT LInac
format: preprint
year: 1993
1 author: R. Zhang
abstract: The plane-wave transformer (PWT) linac, proposed by Swenson, will be used in the Saturnus, the UCLA high gain infrared FEL project. The FEL's output wavelength is designed to match the 10.6 um radiation which CO2 lasers produce....
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title: Memo: Tentative Design of the Waveguide FEL at UCLA
format: preprint
year: 1993
1 author: R. Zhang
abstract: In order to investigate the slippage effects in FELs, we are going to design a millimeter FEL with the following parameters: ....
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title: BPM Revisit: Summary of the Previous Test Results
format: preprint
year: 1993
5 authors: R. Zhang | P. Davis | G. Hairapetian | S. Hartman | S. Park
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title: Two-Stage Chirped-Beam SASE-FEL for High Power Femtosecond X-Ray Pulse Generation
format: preprint
year: December 10, 2001
5 authors: C. Schroeder | J. Arthur | P. Emma | Sven Reiche | C. Pellegrini
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title: The UCLA high gain infrared FEL
format: preprint
year: 1994
4 authors: G. Travish | M. Hogan | C. Pellegrini | J.B. Rosenzweig
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title: First Observation of Luminosity-Driven Extraction Using Channeling with a Bent Crystal
format: preprint
year: 1998
26 authors: A. Asseev | S. I. Baker | S. A. Bogacz | R. A. Biryukov | R.A. Carrigan | D. Chen | D. B. Cline | B. Cox | J. A. Ellison | W. Gabella | V. Golovatyuk | G. Jackson | A. Khanzadeev | A. McManus | N. Mokhov | C.T. Murphy | B. Newberger | T. Prokofieva | S. Ramachandran | J. Rhoades | J.B. Rosenzweig | V. Samsonov | H. J. Shih | G. Solodov | A. Tartin | E. Tsyganov
abstract: Luminosity-driven channeling extraction has been observed for the first time from a 900 GeV circulating proton beam at the Fermilab Tevatron. The extraction efficiency was found to be of he order of 30%. A 150 kHz beam was obtained during luminosity-driven extraction with a tolerable background rate at the collider experiments, and a 900 kHz beam was obtained when background limits were doubled. This is the highest energy at which channeling has been observed.
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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: Pulse Compression in RF Photoinjectors: Applications to Advanced Accelerators
format: preprint
year: 1995
3 authors: J.B. Rosenzweig | N. Barov | E. Colby
abstract: While rf photoinjectors are an excellent source of high brightness electron beams, there are constraints tying together the expected emittance and peak current performance of a given photoinjector system. These constraints, which arise from the complicated dynamics of the electrons due to the interplay of rf and space-charge forces within the photoinjector, tend to favor lowe peak current operation. For some ultimate uses of photoinjector beams, such as linear collider test beams, wake-field accelerators and FELs, one may desire much higher peak currents. In this case, an inexpensive and reliable method for producing extramely short, high-current electron bunches is to use magnetic compression. We examine this scheme alalytically and by computer simulation. Many applications are illustrated, including the TESLA Test Facility/FEL injector, ulta-high current beams for plasma wake-fields, and generation of femtosecond electron pulses for injection into short wavelength laser-based accelerators. It is show that the injection timing jitter associated with the laser can be nearly eliminated using this scheme, making it an indispensable component in many of the advanced acclerator injectors we consider.
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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: Observations, Measurements and Applications of a Steady Collective Mode in an Electron Storage Ring
format: preprint
year: 1998
3 authors: A. Terebilo | C. Pellegrini | M. Cornacchia
abstract: A single bunch of charged particles in a storage ring is a system of 10(9) - 10(11) coupled non-linear oscillators with radiative energy loss and compensated by the accelerating cavity. A stable collective mode in such system was induced and observed in SPEAR storage rign using a turn-by-turn phase space monitor. New possibilities of using this mode as a tool to experimentally study non-linear dynamics in storage rings are discussed.
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title: Electromagnetic Wake-fields and Beam Stability in Slab-symmetric Dielectric Structures
format: preprint
year: 1997
3 authors: A. Tremaine | J.B. Rosenzweig | P. Schoessow
abstract: Several promising schemes for high-gradient acceleration of charged particles in slab-symmetric electromagnetic structures have been recently proposed. In this paper we investigate, by both computer simulation and theoretical analysis, the longitudinal and transverse wake-fields experienced by a relativistic charged particle beam in a planar structure. We show that in the limit of an infinitely wide beam the net deflecting wake-fields vanishes. This result is verified in the limit of a large aspect ratio (sheet) beam by finite beam analysis based on a Fourier decomposition of the current profile, as well as a paraxial wave analysis of the wake-fields driven by Gaussian profile beams. The Fourier analysis forms the basis of an examination of flute instability in the sheet beam system. Practical implications of this result for beam stability and enhanced current loading in short wavelength advanced accelerators 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: 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: Parametric study of an X-ray FEL
format: preprint
year: 1994
7 authors: G. Travish | W. Fawley | K. J. Kim | H. D. Nuhn | C. Pellegrini | H. Winick | M. Xie
abstract: An FEL utilizing a high energy, high current and low emittance beam to produce radiation shorter than 2 AA is investigated in this paper. This device is an extension of the previously proposed 40 AA Linac Coherent Light Source based on the Stanford linear accelerator. Here we investigate the performance characteristics and parameter sensitivities of this single pass, high gain FEL amplifier operating by self-amplified spontaneous emission (SASE). We begin by comparing various approaches to this short wavelength source and justify our choice of a helical undulator operating on the fundamental frequency. Numerical simulations as well as extensions of previous studies are used to show performance as a function of undulator parameters, startup noise, emittance, focusing, current and energy spread. Further studies and parameter modifications are proposed where needed.
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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: 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: Traveling wave undulators for FELs andsynchrotron radiation sources.
format: preprint
year: 2005
1 author: C. Pellegrini
abstract: We study the use of a traveling wave waveguide as an undulator for short wavelength free-electron lasers (FELs) and synchrotron radiation sources. This type of undulator -which we will call TWU- can be useful when a short electron oscillation period and a large aperture for the propagation of the beam are needed. The availability of high power X-band microwave sources, developed for the electron-positron linear collider, make it possible today to build TWUs of practical interest to produce short wavelength radiation from a beam of reduced energy respect to the case of more conventional undulators. In this paper we will discuss the characteristic of the TWU, the systems that can be used to control the effect of RF power losses in the waveguide walls, and how to optimize a TWU and the associated electron transport system for use in a synchrotron radiation source or FEL.
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title: MAFIA Studies of the Plane Wave Tranformer Linac
format: preprint
year: Januray 6, 1992
1 author: S. Hartman
abstract: In designing a high power rf-accelerator one needs to examine any filed disturbances created by asymmetries in teh structure. In the following we present a study of the disturbance of the modes using the three-dimensional frequency domain solver MAFIA[1]. We pay particular attention to perturbations in the accelerating mode and also to higher order modes which can be excited by the electron beam itself. These perturbations in the accelerating mode and off axis kicks due to the higher order modes give rise to emittance growth. Some ideas of how to redesign the support structure in order to iminimze accelerating mode perturbation effects and also of how to damp out unwanted higher order modes are discussed.
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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: Surface Plasmon Enhanced Photoemission
format: preprint
year: March 18, 1993
1 author: S. Hartman
abstract: Photoemission studies have been carried out recently at the UCLA photo injector which cannot be explained by a straight forward application of the standard Fowler-Dubridge (1,2) theory for photoemission. This theory is used to calculate the contributions to the extracted current from field emission, thermal emission and the bulk photoemission process. The Fowler-Dubridge theory predicts a photoyield of 5x10(-6), which is two orders of magnitude less than that observed experimentally at 70 degrees incidence. However, if one assumes optical coupling to surface polasmons via surface roughness. Then one can calculate photoyields of 10(-4) as observed experimentally. Also, if the vector nature of the photoemission process is accounted for then one can calculated photoyields which agree with experimental data as a function of incident illumination angle, polarization angle, and laser wavelength. A few ideas are then set forth on photocathode preparation and materials so as to increase photoyield.
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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: Space Charge Depleted Emission from a Damaged Photocathode
format: preprint
year: February 4, 1993
2 authors: S. Hartman | J.B. Rosenzweig
abstract: There has been a long-standing question about the amount of charge extracted from the UCLA photo-injector as a function of incident laser energy (quantum efficiency). One expects the charge measured at the exit of the rf gun to be a linear function of applied laser energy to the photocathode. However, this is not the case fo the UCLA experiment thus far. However, the quantum efficiency data which measures the total extracted charge out of the rf gun as a function of laser energy, is very non linear. From zero nC to approximately 0.5nC the charge extracted follows a linar trend. From 0.5nC to 3nC the extracted charge falls off unexpectedly. Because of the highly dynamical behaviour of the electron beam near the cathode, a series of PARMELA simulations have been carried out to model the evolution of the beam in this region. These simulations give excellent agreement with the experimental data. Also, a simple model is put forth to explain the physical process which limits the emission of charge.
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title: Space Charge Depleted Emission and Electron Beam Pulse Lengthening from a Damaged Photocathode
format: preprint
year: February 4, 1993
2 authors: S. Hartman | J.B. Rosenzweig
abstract: There have been a long-standing questions about the amount of charge extracted from the UCLA photo-injector as a function of incident laser energy (quantum efficiency), and the observed pulse lengthening in time. One expects the charge measured at the exit of the rf gun to be a linear function of applied laser energy to the photocathode. However, this is not the case for the UCLA experiment thus far. The quantum efficiencey data, which measures the total extracted charge out of the rf gun as a function of laser energy, is very non linear. From zero nC to approximately 0.5 nC the charge extracted follows a linear trend. From 0.5 nC to 3 nC the extracted charge falls off unexpectedly. In addition, streak camera measurements indicate that the beam's temporal length expands considerably from that of the laser. Because of the highly dynamical behavior of the electron beam near the cathode, a series of PARMELA simulations have been carried out to model the evolution of the beam in this region, both in time structure and in maximum allowed charge. These simulations give excellent agreement with the experimental data. Also, a simple model is put forth to explain the physical process which limits the emission of charge.
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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: Space Charge Depleted Emission II: Further Exploration of the Model, and Comparison to Experiment
format: preprint
year: April 1, 1993
2 authors: S. Hartman | J.B. Rosenzweig
abstract: In a previous note (CAA-TEC-NOTE-48), we presented theory and simulation of space charge suppression of the emitted beam charge in from gun. The simple theory, based on calculation of the longitudiinal electric field of the beam and its image charge at teh cathode, explained both the data and the simulation well. The saturation phenomenon of the emitted beam chartge was found to depend only on the applied electric field and the effective emission area of the photoelectrons. The purpose of this note is to further explore the applicability of this theoretical model, and to show that the 70 degree quantum efficiency data quantitatively support the model.
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title: Report on a Visit by American Scientists to UNK Project at IHEP-Protvino
format: preprint
year: January 8, 1993
6 authors: M. Medinnis | C. Pellegrini | Schlein, P. | Sessler, A. M. | Taylor, C. | Reardon, P.
abstract: This document results from a visit to the Institute for High Energy Physics in Protvino, Russia, by a group of U.S. physicists during 13-15 July, 1992. The purpose of the trip, which was supported by the U.S. National Science Foundation, was to learn about the state of the UNK superconducting 3 TeV accelerator complex and also to understand the cost and magnitude of the task required to complete the machine. If completed, UNK could provide a unique High Energy Physics facility. First, a collider version could serve as an excellent Factory to study the decay of Beauty particles. Secondly, the 3 TeV proton beam may be the highest energy available for a fixed target physics program. Although the superconducting magnet design is mature and tests have been successful, severe budget cutbacks have brought the project to a virtual halt. A realistic goal for IHEP may be the expeditious completion of UNK-1, the 600 GeV booster ring, in parallel with the pursuit of international collaboration on fiscal, technical and management support for the 3 TeV project.
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title: Gain Computation
format: preprint
year: April 24, 2002
1 author: Sven Reiche
abstract:
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title: SUPERFLIC - A Recirculating Superconducting Linear Collider Top Factory
format: preprint
year: May 28, 1991
1 author: J.B. Rosenzweig
abstract:
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title: Analogies Between Charged Particle Beams and Photon Beams: Simple Methods for Laboratory Use
format: preprint
year: October 25, 1991
1 author: J.B. Rosenzweig
abstract:
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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: 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: 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: 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: A Tapered Dielectric Structure for Laser Acceleration at Low Energy
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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
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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: Initial Results on Electron Beam Generation Using Pyroelectric Crystals
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year:
6 authors: E.R. Arab | D. Fong | U.H. Lacroix | G. Travish | N. Vartanian | R.B. Yoder
abstract: The Micro-Accelerator Platform is an optical-wavelength microstructure for laser acceleration of particles, currently under development at UCLA. It is a slab-symmetric structure and can be constructed in layers using existing nanofabrication techniques. We present several possible fabrication techniques and preliminary experimental outcomes for manufacturing this structure.
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