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| PLT33 |
Summary of WG3 – Free Electron Lasers
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- Z. Huang
SLAC, Menlo Park, California
- L. Serafini
INFN-Milano, Milano
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Summary of the Free Electron Lasers Working Group
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Slides
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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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| WG332 |
Fully Coherent X-Ray Pulses from a Regenerative-Amplifier FEL
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- Z. Huang, R. D. Ruth
SLAC, Menlo Park, California
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We propose and analyze a regenerative-amplifier FEL to produce fully coherent, hard X-ray pulses [1]. The method makes use of narrow-bandwidth Bragg crystals to form an X-ray feedback loop around a relatively short undulator. Self-amplified spontaneous emission (SASE) from the leading electron bunch in a bunch train is spectrally filtered by the Bragg reflectors and is brought back to the beginning of the undulator to interact repeatedly with subsequent bunches in the bunch train. The FEL interaction with these short bunches regeneratively amplifies the radiation intensity and broadens its spectrum, allowing for effective transmission of the X-rays outside the crystal bandwidth. The spectral brightness of these X-ray pulses is about 2 to 3 orders of magnitude higher than that from a single-pass SASE FEL.
[1] Z. Huang and R. Ruth, Phys. Rev. Lett. 96, 144801 (2006).
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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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