| title: | Successful beam-beam tuneshift compensation |
| format: | thesis |
| year: | 2005 |
| authors: | Kip Bishofberger |
| abstract: | The performance of synchrotron colliders has been limited by the beam-beam limit, a maximum tuneshift that colliding bunches could sustain. Due to bunch-to-bunch tune variation and intra-bunch tune spread, larger tuneshifts produce severe emittance growth. Breaking through this constraint has been viewed as impossible for several decades. A device known as the Tevatron Electron Lens (TEL) has been designed, constructed, and tested in the Tevatron at Fermilab. This device produces a pulsed beam of electrons which interact with the antiproton bunches in the Tevatron. The peak beam current is typically 2 A, and the beam energy can range from 4 keV to 12 keV. The bunches interact with the beam’s electromagnetic field, causing their tunes to shift opposite to the beam-beam limit. By tailoring the electron-beam current for each bunch, the tuneshift can be individualized to compensate for the adverse bunch-to-bunch variation. Additionally, shaping the electron-beam profile shifts the tune of each antiproton within each bunch selectively depending on their amplitude, compensating for the intra-bunch tune spread. The typical tuneshift that each antiproton feels is 0.0097 per interaction point, and the bunch-to-bunch tune variation is approximately 0.007. The tune spread within each bunch is expected to be about 0.004. Experiments with the TEL yielded tuneshifts with proton bunches equal to 0.0089, which is equivalent to antiproton tuneshifts of 0.0112. This value is more than necessary to successfully compensate the beam-beam interactions. Additionally, the use of the TEL has significantly reduced antiproton losses and emittance growth, evidence that such compensation is indeed beneficial to synchrotron operation. This dissertation introduces the physics of ultra-relativistic synchrotrons and low-energy electron beams, with emphasis placed on the limits of the Tevatron and the needs of a tuneshift-compensation device. A detailed analysis of the TEL is given, comparing theoretical models to experimental data whenever possible. Finally, results of Tevatron operations with inclusion of the TEL are presented and analyzed. It is shown that the TEL provides a way to shatter the previously inescapable beam-beam limit. |
| title: | An adjustable short-focal length, high-gradient PMQ electron-beam final-focus system for the PLEIADES ultra-fast x-ray Thomson source |
| format: | thesis |
| year: | |
| authors: | Jae Lim |
| abstract: | In the span of a 100 year since the discovery of first x-rays by Roentgen that won him the ¯rst Nobel prize in physics, several types of radiation sources have been developed. Currently, radiations at extremely short wavelengths have only been accessed at synchrotron radiation sources. However, the current 3rd generation synchrotron sources can only produce x-rays of energy up to 60 keV and pulse lengths of several picoseconds long. But needs for shorter wavelength and shorter pulse duration radiations demanded by scientists to understand the nature of matter at atomic/molecular scale initiated the new scienti¯c research for the production of sub-picosecond, hard x-rays. At the Lawrence Livermore National Laboratory, a Thomson x-ray source in the backscattering mode {a head-on collision between a high intensity Ti:Sapphire Chirped Pulse Amplification laser and a relativistic electron beam { called the PLEIADES (Picosecond Laser-Electron Inter-Action for the Dynamical Evaluation of Structures) laboratory has been developed. Early works demonstrated the production of quasi-monochromatic, femto-second long, hard x-rays. Initially reported x-ray flux was in the low range of 10^5 photons per shot. During the early stage of PLEIADES experiments, 15 T/m electromagnet final focusing quadrupoles (in a triplet lattice con¯guration) were employed to focus the beam to a 40-50 ¹m spot-size. A larger focal spot-size beam has a low-density of electron particles available at the interaction with incident photons, which leads to a low scattering probability. The current dissertation shows that by employing a 560 T/m PMQ (Permanent-Magnet Quadrupole) ¯nal focus system, an electron beam as small as 10-20 ¹m can be achieved. The implementation of this final focus system demonstrated the improvement of the total x-ray flux by two orders of magnitude. The PMQ ¯nal focus system also produced small electron beams consistently over 30-100 MeV electron beam energy, which enabled the production of x-ray energy over 40-140 keV. In this dissertation, the PLEIADES Thomson x-ray facility will be described in detail includes the 100 MeV linac and the FALCON laser system. Later, we will discuss the design, construction and implementation of the PMQ final focus system in the beamline. The measurement of electron beam parameters before and after the final focus system will be presented. The beam measurements at the interaction region were accomplished with the use of both OTR (Optical Transition Radiation) imaged by a CCD camera and the fast streak camera for respective spatial and temporal alignments. The theoretical analysis in real beam" effects and spacetime beam jitter e®ects will be given to help understand the observations. A 3D simulation tool developed for x-ray data analysis was used to provide direct comparisons with the x-ray °ux, spectrum distribution and transverse x-ray profile. |
| title: | Experimental and Analytical Study of a High Gain Self Amplified Spontaneous Emission Free Electron Laser Operating in a Large Spectral Bandwidth Regime |
| format: | thesis |
| year: | 2005 |
| authors: | Gerard Andonian |
| abstract: | The drive to create and measure ultra-short pulses in the x-ray regime advances the ongoing development of free electron lasers (FEL). Several proposed schemes, to shorten the pulse length of the radiation, involve driving the FEL with a chirped (linear longitudinal phase space correlation) electron beam in the self amplified spontaneous emission (SASE) mode. This dissertation examines the experiments conducted under such conditions, canvassing analytical and numerical studies of beam dynamics and radiation properties, experimental observations, and descriptions of the development of novel diagnostics. The VISA (Visible-Infrared SASE Amplifier) program has achieved saturation at 840 nm within a 4 m long undulator. A novel bunch compression mechanism during transport was discovered and ultimately responsible for the high peak current required to drive the FEL. Start-to-end simulations, detailing the dynamics from electron beam inception at the photocathode to the FEL radiation properties at the undulator, were successfully benchmarked to observable data. |
| title: | RESULTS FROM THE UCLA/FNPL UNDERDENSE PLASMA LENS EXPERIMENT |
| conference: | Erice 2005 |
| year published: | 2006 |
| year authored: | 2005 |
| authors: | M. THOMPSON,H. BADAKOV,J. ROSENZWEIG,G. TRAVISH,H. EDWARDS,R. FLILLER,G. 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 µm 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 alsoimaged into a streak camera in order to directly measure the correlation between z and ?r within the beam. |
| title: | Mitigation of RF Gun Breakdown by Removal of Tuning Rods in High Field Regions |
| conference: | Erice 2005 |
| year authored: | 2005 |
| authors: | A.M Cook,J.B Rosenzweig,M. Dunning,P. Frigola,K. Serratto |
| 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. |
| title: | Dielectric Wakefield Accelerating Structure as a Source of Terahertz Coherent Cerenkov Radiation |
| conference: | |
| year authored: | 2006 |
| 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. |
| title: | Experiment to Measure Ramped Electron Bunches at the UCLA Neptune Laboratory Using a Transverse Deflecting Cavity |
| conference: | 12th Advanced Accelerator Concepts Workshop |
| year: | 2006 |
| authors: | R. England,D. Alesini,B. O'Shea,J. Rosenzweig,and 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. |
| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| conference: | |
| year: | 2004 |
| authors: | J.B Rosenzweig,S. Hoover,M.J Hogan,P. Muggli,M. Thompson,G. Travish,R. 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. |
| title: | LIMITS ON PRODUCTION OF NARROW BAND PHOTONS FROM INVERSE COMPTON SCATTERING |
| conference: | |
| year published: | 2006 |
| year authored: | 2005 |
| authors: | J.B ROSENZWEIG,A.M COOK,M. DUNNING,R.J ENGLAND,P. MUSUMECI,M. BELLAVEGLIA,M. BOSCOLO,L. CATANI,A. CIANCHI,G. PIRRO,M. FERRARIO,D. FILLIPETTO,G. GATTI,L. PALUMBO,L. SERAFINI,C. VICARIO,S. JONES |
| 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. |
| title: | EXPERIMENTAL TESTING OF DYNAMICALLY OPTIMIZED PHOTOELECTRON BEAMS |
| conference: | Erice 2005 |
| year published: | 2006 |
| year authored: | 2005 |
| authors: | J.B ROSENZWEIG,A.M COOK,M. DUNNING,R.J ENGLAND,P. MUSUMECI,M. BELLAVEGLIA,M. BOSCOLO,L. CATANI,A. CIANCHI,G. PIRRO,M. FERRARIO,D. FILLIPETTO,G. GATTI,L. PALUMBO,L. SERAFINI,C. VICARIO,S. JONES |
| 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 |
| title: | PRELIMINARY RESULTS FROM THE UCLA/SLAC ULTRA-HIGH GRADIENT CERENKOV WAKEFIELD ACCELERATOR EXPERIMENT |
| conference: | Erice 2005 |
| year: | 2005 |
| authors: | M. THOMPSON,H. BADAKOV,J. ROSENZWEIG,G. TRAVISH,M. HOGAN,R. ISCHEBECK,N. KIRBY,P. MUGGLI,A. SCOTT,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. |
| title: | A Helical Undulator Wave-guide Inverse Free-Electron Laser |
| conference: | |
| year: | 2004 |
| authors: | J. Rosenzweig,N. Bodzin,P. Frigola,C. Joshi,P. Musumeci,C. Pellegrini,S. Tochitsky,and 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. |
| title: | Working Group 2 Summary: Diagnostics and Beam Manipulation |
| format: | talk |
| year: | 2005 |
| authors: | G. Travish |
| abstract: | A summary presentation of working group 2 of the ICFA Workshop of High Brightness Beams. The working group included talks on beam diagnostics and beam manipulation. |
| title: | Beam compression experiments using the UCLA/ATF compressor |
| conference: | |
| year: | 2006 |
| authors: | J.B ROSENZWEIG,M. DUNNING,E. HEMSING,G. ANDONIAN,A.M COOK,A. MUROKH,S. REICHE,D. SCHILLER,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. |
| title: | Limits on production of narrow band photons from inverse Compton scattering |
| conference: | |
| year: | 2006 |
| authors: | J. Rosenzweig,O. 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 |
| title: | Beam Dynamics in a Hybrid Standing Wave-Traveling Wave Photoinjector |
| conference: | |
| year: | 2006 |
| authors: | J.B Rosenzweig,D. Alesini,A.Boni A.Boni,M. Ferrario,L. Ficcadenti,A.Fukusawa A.Fukusawa,A.Mostacci A.Mostacci,B.O’Shea B.O’Shea,L. Palumbo,B.Spataro B.Spataro,V.Fusco 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. |
| title: | An Inverse Compton Scattering Radiation Source via Self-Guiding in a Plasma |
| conference: | |
| year: | 2006 |
| authors: | R. Yoder,J. 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 µm) 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. |
| title: | RF Design of the UCLA/INFN Hybrid SW/TW Photoinjector |
| conference: | |
| year: | 2006 |
| authors: | Brendan O'Shea,J.B Rosenzweig,Alessandro Boni,Atsushi Fukasawa,David Alesini,Massimo Ferrario,Bruno Spataro,Luca Ficcadenti,Andrea Palumbo |
| 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 today’s requirements and is scalable in design to meet tomorrow’s 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 SWand TWsystems 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, εn,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. |
| title: | Emittance compensation with dynamically optimized photoelectron beam profiles |
| journal: | Nuclear Instruments and Methods in Physics Research A |
| vol-pages: | 57:87 |
| year: | 2005 |
| authors: | J. Rosenzweig,A. 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’s longitudinal extrema. These nonlinearities are known to produce both transverse and longitudinal emittance growth. On the other hand, it has recently been shown by Luiten that by illuminating the cathode 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 recent photoinjectors. It is seen that the two processes are compatible, with simulations indicating a very high brightness beam can be obtained. The robustness of this scheme to systematic errors is examined. Prospects for experimental tests of this scheme are discussed. |
| title: | High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser |
| journal: | Physical Review Letters |
| vol-pages: | 94:154801 |
| year: | |
| authors: | P. Musumeci,S.Ya Tochitsky,S. Boucher,C. Clayton,A. Doyuran,R. England,C. Joshi,C. Pellegrini,J. Ralph,J. Rosenzweig,C. Sung,S. Tolmachev,G. Travish,A. Varfolomeev,A. Jr.,T. Yarovoi,R. 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. |
| title: | Side-coupled slab-symmetric structure for high-gradient acceleration using terahertz power |
| journal: | Physical Review Special Topics - Accelerators and Beams |
| vol-pages: | 8:111301 |
| year: | 2005 |
| authors: | R. Yoder,J. 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. |
| title: | Pulsed-laser nonlinear Thomson scattering for general scattering geometries |
| journal: | Physical Review E |
| vol-pages: | 72:056502 |
| year: | 2005 |
| authors: | G. Krafft,A. Doyuran,J. 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. |
| title: | Effects of Ion Motion in Intense Beam-Driven Plasma Wakefield Accelerators |
| journal: | Physical Review Letters |
| vol-pages: | 95:195002 |
| year: | 2005 |
| authors: | J. Rosenzweig,A. Cook,A. Scott,M. Thompson,R. Yoder |
| abstract: | Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear have included intense electron beams with densities many times in excess of the plasma beam’s electric fields expel the plasma electrons from the beam path to many beam radii in We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are Implications of ion motion on the feasibility of the PWFA-based colliders are discussed. |
| title: | Higher harmonic inverse free-electron laser interaction |
| journal: | Physical Review E |
| vol-pages: | |
| year: | 2005 |
| authors: | P. Musumeci,C. Pellegrini,J. 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. |