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| WG312 |
Optical Klystron Enhancement to SASE X-ray FELs
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- Z. Huang, Y. T. Ding, P. Emma
SLAC, Menlo Park, California
- V. Kumar
ANL, Argonne, Illinois
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We study the optical klystron enhancement to SASE FELs in theory and simulations. In contrast to a seeded FEL, the optical klystron gain in a SASE FEL is not sensitive to any phase mismatch between the radiation and the microbunched electron beam. The FEL performance with the addition of four optical klystrons located at the undulator long breaks in the Linac Coherent Light Source (LCLS) shows significant improvement if the uncorrelated energy spread at the undulator entrance can be controlled to a very small level. In addition, FEL saturation at shorter X-ray wavelengths (around 1.0 Angstrom) within the LCLS undulator length becomes possible.
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Slides
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| WG313 |
Beam Physics Highlights of the FERMI@ELETTRA Project
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- S. Di Mitri, M. Cornacchia, P. Craievich, G. Penco, M. Trovo
ELETTRA, Basovizza, Trieste
- P. Emma, Z. Huang, J. Wu
SLAC, Menlo Park, California
- D. Wang
MIT, Middleton, Massachusetts
- A. Zholents
LBNL, Berkeley, California
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The electron beam dynamics in the Fermi Linac has been studied in the framework of the design of a single-pass free electron laser (fel) based on a seeded harmonic cascade. The wakefields of some accelerating sections represent a challenge for the preservation of a small beam emittance and for achieving a small final energy spread. Various analytical techniques and tracking codes have been employed in order to minimize the quadratic and the cubic energy chirps in the longitudinal phase space, since they may cause a degradation of the fel bandwidth. As for the transverse motion, the beam breakup (bbu) instability has been recognized as the main source of emittance dilution; the simulations show the validity of local and non-local correction methods in order to counteract the typical “banana” shape distortion of the beam caused by the instability.
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Slides
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| WG423 |
Transverse to Longitudinal Emittance Exchange to Improve Performance of High-Gain X-Ray Free Electron Laser
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- K.-J. Kim
ANL, Argonne, Illinois
- P. Emma, Z. Huang
SLAC, Menlo Park, California
- P. Piot
Northern Illinois University, DeKalb, Illinois
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The ability to generate small transverse emittance is a limiting factor for the performance of high-gain free electron lasers for X-rays. Noting that beams from an RF photocathode gun can have energy spread much smaller than that required for an X-ray FEL, we present a method to produce a normalized transverse emittance 0.1 mm·mrad, an order of magnitude smaller than the state-of-the-art. The method consists of producing a pancake-shaped beam of emittance (1, 1, 0.1) mm·mrad in the (x-,y-,z-)direction, applying the flat beam technique [1] to obtain (10, 0.1, 0.1) mm·mrad, and then exchanging the x-emittance with the longitudinal(z)-emittance, finally obtaining (0.1, 0.1, 10) mm·mrad. We show that the space charge effect does not degrade the small longitudinal emittance of the pancake-shaped beam. We found that the optical scheme studied previously [2] for an approximate longitudinal-transverse exchange is not adequate for the present case due to the large emittance ratio. However, we found a new scheme giving rise to an exact exchange necessary for the method. Results of preliminary simulation confirm the analytical theory.
[1] R. Brinkmann, Ya Derbenev, and K. Floettmann, Phys. Rev. ST Acc. Beams 4, 053501 (2001)
[2] M. Cornacchia and P. Emma, Phys. Rev. ST Acc. ST-AB 7 074401 (2004)
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Slides
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| WG502 |
Feedback Concepts: Experience at SPPS, LCLS Plans
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- P. Krejcik, S. Allison, P. Emma, D. Fairley, J. Wu
SLAC, Menlo Park, California
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The LCLS will operate with single bunches at a repetition rate of 120 Hz. The control system is designed to measure and respond to beam errors within the 8.3 ms between pulses. Single-shot, high-resolution measurements of the beam position are required for trajectory feedback control as well as beam energy control in the bunch compressor chicanes and dog-leg beam lines. A single-shot measurement of the bunch length at the exit of bunch compressor chicanes is also required to provide full feedback control of the longitudinal phase space. The amplitude and phases of linac klystrons are controlled pulse-by-pulse within one global feedback loop to maintain the correct energy and bunch length of the beam. The bunch length is determined from measurements of the coherent radiation of the beam, but the type of detector employed varies with bunch length at each location and hence wavelength of the coherent radiation. Experience has been gained with single-shot pyroelectric detectors at the SLAC Sub-Picosecond Pulsed Source (SPPS) and simple feedback control was implemented to stabilize the bunch length. The plans for implementing a full feedback system at LCLS will also be presented.
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