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| THOPA01 |
Formation of Electron Bunches for Harmonic Cascade X-ray Free Electron Lasers
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2738 |
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- M. Cornacchia, S. Di Mitri, G. Penco
ELETTRA, Basovizza, Trieste
- A. Zholents
LBNL, Berkeley, California
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A relatively long electron bunch is required for an operation of harmonic cascade free electron lasers (FELs). This is because they repeatedly employ a principle when the radiation produced in one cascade by one group of electrons proceeds ahead and interacts with other electrons from the same electron bunch in the next cascade. An optical laser is used to seed the radiation in the first cascade. Understandably the length of the electron bunch in this situation must accommodate the length of the x-ray pulse multiplied by a number of cascades plus a time jitter between the arrival time of the electron bunch and a seed laser pulse. Thus a variation of the peak current along the electron bunch as well as slice energy spread and emittance may affect the performance of the FEL. In this paper we analyze all possible sources affecting the distributions and interplay between them and show how desirable distributions can be produced. Results are illustrated with simulations using particle tracking codes.
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Transparencies
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| THPLS092 |
Nb-Pb Superconducting RF-Gun
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3493 |
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- J.S. Sekutowicz, J.I. Iversen, D. Klinke, D. Kostin, W.-D. Möller
DESY, Hamburg
- I. Ben-Zvi, A. Burrill, T. Rao, J. Smedley
BNL, Upton, Long Island, New York
- M. Ferrario
INFN/LNF, Frascati (Roma)
- P. Kneisel
Jefferson Lab, Newport News, Virginia
- K. Ko, L. Xiao
SLAC, Menlo Park, California
- J. Langner, P. Strzyzewski
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
- R.S. Lefferts, A.R. Lipski
SBUNSL, Stony Brook, New York
- J.B. Rosenzweig
UCLA, Los Angeles, California
- K. Szalowski
University of Lodz, Lodz
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We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.
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| THPLS093 |
Status of the Photocathode RF Gun System at Tsinghua University
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3496 |
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- X. He, Cheng. Cheng. Cheng, Q. Du, Du.Taibin. Du, Y.-C. Du, W.-H. Huang, Y. Lin, C.-X. Tang, S. Zheng
TUB, Beijing
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An S-band high gradient photocathode RF gun test stand is in construction process at Tsinghua University. The photocathode RF gun test stand is a primary step of a femtosecond hard x-ray source based on Thomson scattering. The photocathode RF gun system adopts Ti:Sap laser, BNL IV type 1.6 cell RF gun, compact compensation solenoid. We foresee to conduct investigations on the thermal emittance contribution of surface roughness, the emittance compensation technique under various laser shape and its application to Thomson scattering x-ray source. Except for the transportation of laser, correction of laser front for glazing incidence and laser pulse shaping system, other parts of the photocathode RF gun test stand have been constructed, and we can start very primary experiment on the RF gun test stand, such as measurements of dark current, QE and energy of the beam. The experimental results are reported.
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| THPLS094 |
First Measurement Results at the LEG Project's 100 keV DC Gun Test Stand
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3499 |
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- S.C. Leemann, Å. Andersson, R. Ganter, V. Schlott, A. Streun, A.F. Wrulich
PSI, Villigen
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The Low Emittance Gun Project (LEG) at PSI aims at developing a high-brightness, high-current electron source: a 20-fold improved brightness compared to present state-of-the-art electron guns. The source is intended to form the basis for a cost-efficient implementation of a high-power X-ray FEL light-source for scientific research at PSI. A field emitter array (FEA) cathode is being considered a source candidate. In order to study pulsed field emission from such a cathode and to investigate space charge compensation techniques as well as to develop diagnostic procedures to characterize the beam resulting from an FEA cathode, a 100 keV DC gun test stand has been built. The test stand gun and diagnostics have been modeled with the codes MAFIA and GPT. From extensive parameter studies an optimized design has been derived and construction of the gun and diagnostics have recently been completed. We report on the commissioning of the test stand and present first measurement results.
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| THPLS098 |
Optimum Beam Creation in Photoinjectors Using Space-charge Expansion
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0 |
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- J.B. Rosenzweig, A.M. Cook, M.P. Dunning, C. Pellegrini
UCLA, Los Angeles, California
- M. Boscolo, M. Ferrario, D. Filippetto, L. Palumbo, C. Vicario
INFN/LNF, Frascati (Roma)
- P. Musumeci
INFN-Roma, Roma
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It has recently been shown by Luiten* that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for an experiment at the SPARC injector at Frascati in 2006. We review preparations for this experiment, and discuss the measurable quantities and their appropriate diagnosis, including the time-resolved observation of ellipsoidal beam shape at low energy. A scheme based on gating of Cerenkov radiation produced at an Aerogel for time-resolved measurements is proposed. Future measurements at high energy based on fs resolution RF sweepers are discussed. The prospects for using the very low longitudinal emittance beam in a future bunch compressor for producing 10 micron long beams are evaluated.
*O. J. Luiten et al. Physical Review Letters, 93, 094802-1 (2004).
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