Emma, P.

Paper	Title	Page
MOBAU04	Optical Klystron Enhancement to SASE X-Ray FELs	29
	Y. T. Ding, P. Emma, Z. Huang SLAC, Menlo Park, California V. Kumar RRCAT, Indore (M. P.)
	The optical klystron enhancement to self-amplified spontaneous emission (SASE) free electron lasers (FELs) is studied in theory and in 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. We also discuss the application of the optical klystron in a compact x-ray FEL design that employs relatively low electron beam energy together with a shorter-period undulator.
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MOPPH054	FERMI @ Elettra: A Seeded FEL Facility for EUV and Soft X-Rays	166
	J. N. Corlett, L. R. Doolittle, W. M. Fawley, S. M. Lidia, G. Penn, I. V. Pogorelov, J. Qiang, A. Ratti, J. W. Staples, R. B. Wilcox, A. Zholents LBNL, Berkeley, California E. Allaria, C. J. Bocchetta, D. Bulfone, F. C. Cargnello, D. Cocco, P. Craievich, G. D'Auria, M. B. Danailov, G. De Ninno, S. Di Mitri, B. Diviacco, M. Ferianis, A. Galimberti, A. Gambitta, M. Giannini, F. Iazzourene, E. Karantzoulis, M. Lonza, F. M. Mazzolini, G. Penco, L. Rumiz, S. Spampinati, G. Tromba, M. Trovo, A. Vascotto, M. Veronese, M. Zangrando ELETTRA, Basovizza, Trieste M. Cornacchia, P. Emma, Z. Huang, J. Wu SLAC, Menlo Park, California W. Graves, F. X. Kaertner, D. Wang MIT, Middleton, Massachusetts
	We describe the conceptual design and major performance parameters for the FERMI FEL project funded for construction at the Sincrotrone Trieste, Italy. This user facility complements the existing storage ring light source at Sincrotrone Trieste, and will be the first facility to be based on seeded harmonic cascade FELs. Seeded FELs provide high peak-power pulses, with controlled temporal duration of the coherent output allowing tailored x-ray output for time-domain explorations with short pulses of 100 fs or less, and high resolution with output bandwidths of the order of meV. The facility uses the existing 1.2 GeV S-band linac, driven by electron beam from a new high-brightness rf photocathode gun, and will provide tunable output over a range from ~100 nm to ~10 nm, and APPLE undulator radiators allow control of x-ray polarization. Initially, two FEL cascades are planned, a single-stage harmonic generation to operate over ~100 nm to ~40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelengh, each with spatially and temporally coherent output, and peak power in the GW range.
THBAU02	Electron Beam Alignment Strategy in the LCLS Undulators	529
	H.-D. Nuhn, P. Emma, G. L. Gassner, C. M. LeCocq, F. Peters, R. E. Ruland SLAC, Menlo Park, California
	The x-ray FEL process puts very tight tolerances on the straightness of the electron beam trajectory (2 μm rms) through the LCLS undulator system. Tight but less stringent tolerances of 80 μm rms vertical and 140 μm rms horizontally are to be met for the placement of the individual undulator segments with respect to the beam axis. The tolerances for electron beam straightness can only be met through beam-based alignment (BBA) based on electron energy variations. Conventional alignment will set the start conditions for BBA. Precision-fiducialization of components mounted on remotely adjustable girders and the use of beam-finder wires (BFW) will enable to satisfy placement tolerances. Girder movement due to ground motion and temperature changes will be monitored continuously by an alignment monitoring system (ADS) and remotely corrected. This stabilization of components as well as the monitoring and correction of the electron beam trajectory based on BPMs and correctors will increase the time between BBA applications. Undulator segments will be periodically removed from the undulator Hall and measured to monitor radiation damage and other effects that might degrade undulator tuning.
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THBAU05	Precision Measurement of the Undulator K Parameter using Spontaneous Radiation	548
	J. J. Welch, J. Arthur, P. Emma, J. B. Hastings, Z. Huang, H.-D. Nuhn, P. Stefan SLAC, Menlo Park, California R. M. Bionta LLNL, Livermore, California R. J. Dejus, B. X. Yang ANL, Argonne, Illinois
	Obtaining a precise and uniform value of the undulator parameter, K, over the full undulator length is critical for producing high-gain FEL radiation, especially in a hard x-ray source such as the LCLS. At an FEL wavelength of 1.5-Å the relative variation of K over the full undulator must be (dK/K)rms < 0.015%. Transverse misalignments, construction errors, radiation damage, and temperature variations all contribute to a different K value in each few-meter-long undulator segment. It is therefore important to measure relative K precisely, after installation and alignment, using beam-based techniques, if possible. We propose a fairly simple method using the angle-integrated spontaneous radiation spectrum of two interfering undulators, and the natural shot-to-shot energy centroid jitter of the electron beam, to measure the relative K error between two segments using both ideal and measured undulator fields. By 'leap-frogging' to different pairs of undulators with extended separations we hope to confirm or correct the value of K, including proper tapering, over the entire 130-m long FEL undulator.
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