FERMI@Elettra: A seeded FEL facility for EUV and soft X-rays

We describe the conceptual design and major performance parameters for the FERMI@Elettra Free Electron Laser (FEL) project funded for construction at 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.