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AAC 2006 12th

Name: AAC 2006 12th

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Date: 2006-01-01

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8 papers from the conference:

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: 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: 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: 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.
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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: 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: 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: 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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