Zholents, A.

Paper	Title	Page
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.
THAAU01	Output Bandwidth Effects in Seeded, Harmonic Cascade FELs	500
	W. M. Fawley, G. Penn, A. Zholents LBNL, Berkeley, California
	A number of laboratories are studying and/or proposing seeded Harmonic Cascade (HC) FELs as a means both to reach soft x-ray output wavelengths and to provide a degree of longitudinal coherence much greater than that normally possible with SASE devices. While theoretically the output bandwidth of a HC FEL can approach the transform limit given a high quality input seed of reasonable power, there appear to be a number of practical considerations that in many cases can increase the output bandwidth many-fold. In particular, designs that employ dispersive sections following modulator sections in order to increase the amount of coherent harmonic microbunching, can be very sensitive to temporal variations in the electron beam energy, resulting in an output wavelength chirp. Unwanted microbunching induced by the combination of longitudinal space charge instability growth in the linac and CSR in compression sections also can lead to variations in the output radiation phase and amplitude, thus increasing the bandwidth. We give some semi-analytical results for the predicted bandwidth increase for HC configurations and also some detailed numerical simulation results.
	Slides
	Talk
THPPH059	Energy Modulation of the Electrons by the Laser Field in the Wiggler Magnet: Analysis and Experiment	725
	K. Holldack BESSY GmbH, Berlin A. Zholents LBNL, Berkeley, California
	Energy modulation of the electron beam after the interaction with the laser field in the wiggler magnet can be calculated using interference of the laser field and the field of spontaneous emission in the far field region of wiggler radiation. Quite often this approach gives a deeper insight on the process than traditional calculations where the effect of the laser field on the electron energy is integrated along the electron trajectory in the wiggler. We demonstrate it by showing the agreement between the analytical model and the experiment involving wiggler scan measurements with large detuning from the FEL resonance producing more than one order of magnitude variations in the amplitude of the energy modulation. The high sensitivity was achieved using the THz radiation from a sub-mm density variations that energy modulated electron leave behind while propagating the storage ring lattice. All measurements were performed at the BESSY-II electron storage ring.