• S. Di Mitri, P. Craievich
  ELETTRA, Basovizza, Trieste
• M. Cornacchia, P. Emma, Z. Huang, J. Wu
  SLAC, Menlo Park, California
• D. Wang
  MIT, Middleton, Massachusetts
• A. Zholents
  LBNL, Berkeley, California

Funding: Sincrotrone Trieste and Director, Office of Science, of the U.S. Department of Energy, under contract No. DE-AC03-76SF00098.

Design studies are in progress to use the existing FERMI@Elettra linear accelerator for a seeded harmonic cascade FEL facility [1]. This accelerator will be upgraded to 1.2 GeV and equipped with a low-emittance RF photocathode gun, laser heater, two bunch compressors, and beam delivery system. We present an optimization study for all the components following the gun, with the aim of achieving high peak current, low energy spread and low emittance electron beam necessary for the FEL. Various operational scenarios are discussed. Results of accelerator simulations including effects of space charge, coherent synchrotron radiation, and wakefields are reported.

[1] C. Bocchetta, et al., FERMI@Elettra - A Seeded Harmonic Cascaded FEL for EUV and Soft X-rays, this conference.

• P. Craievich, S. Di Mitri
  ELETTRA, Basovizza, Trieste

The FEL project FERMI@ELETTRA will use the existing Linac, upgraded to 1.2 GeV, to produce VUV radiation between 100-10 nm. FEL operations require a high quality beam in terms of the bunch energy spread and emittance. In this paper we present an analytical study based on a continuum model to describe the transverse motion of a single bunch. Such a study allows predicting the emittance growth under the combined influence of short-range transverse wakefields, injection offset, initial emittance and misaligned accelerating sections. We also report a comparison between analytical and numerical (tracking code) results.

• M. Ferianis, P. Craievich, G. D'Auria, S. Di Mitri
  ELETTRA, Basovizza, Trieste
• P. Emma
  SLAC, Menlo Park, California
• W. Graves
  MIT, Middleton, Massachusetts
• M. Poggi
  INFN/LNL, Legnaro, Padova
• A. Zholents
  LBNL, Berkeley, California

Fermi is the fourth generation light source currently under design at ELETTRA: based on the Harmonic Generation (HG) scheme it will generate FEL radiation in the 100-10nm range. The successful implementation of the HG scheme calls also for precise knowledge of electron beam emittances and energy spread as well as for very accurate control on the photon to electron interaction, in the Undulator sections. In this paper we present our design for two fundamental Diagnostics foreseen for the new FERMI LINAC: the Beam Position Monitors (BPM) and the Transverse Deflecting cavity set-up. Sensitivity studies on transverse beam displacement effects on global stability of FEL output radiation dictate the ultimate performance to be provided by the BPM system. Due to non negligible longitudinal occupancy of a cavity type BPM, some efforts have been put to study compact cavity BPM configuration. A proper set-up of RF deflecting cavity combined with the vertical ramp foreseen at the end of the LINAC provide a powerful tool for multiple beam measurement. Furthermore, by implementing the two bunch compressors in the vertical plane the effect of the Coherent Synchrotron Radiation (CSR) on the vertical emittance can be checked for.

• C.J. Bocchetta, D. Bulfone, P. Craievich, G. D'Auria, M.B. Danailov, G. De Ninno, S. Di Mitri, B. Diviacco, M. Ferianis, A. Gomezel, F. Iazzourene, E. Karantzoulis, G. Penco, M. Trovo
  ELETTRA, Basovizza, Trieste
• J.N. Corlett, W.M. Fawley, S.M. Lidia, G. Penn, A. Ratti, J.W.  Staples, R.B. Wilcox, A. Zholents
  LBNL, Berkeley, California
• M. Cornacchia, P. Emma, Z. Huang, J. Wu
  SLAC, Menlo Park, California
• W. Graves, F.O. Ilday, F.X. Kaertner, D. Wang, T. Zwart
  MIT, Middleton, Massachusetts
• F. Parmigiani
  Universita Cattolica-Brescia, Brescia

We describe the machine layout and major performance parameters for the FERMI FEL project funded for construction at Sincrotrone Trieste, Italy. The project will be the first user facility based on seeded harmonic cascade FELs, providing controlled, high peak-power pulses. With a high-brightness rf photocathode gun, and using the existing 1.2 GeV S-band linac, the facility will provide tunable output over a range from ~100 nm to ~10 nm, with pulse duration from 40 fs to ~ 1ps, and with fully variable output polarization. Initially, two FEL cascades are planned; a single-stage harmonic generation to operate > 40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelength. The output is spatially and temporally coherent, with peak power in the GW range. Lasers provide modulation to the electron beam, as well as driving the photocathode and other systems, and the facility will integrate laser systems with the accelerator infrastructure, including a state-of-the-art optical timing system providing synchronization of rf signals, lasers, and x-ray pulses. Major systems and overall facility layout are described, and key performance parameters summarized.