Design of an ECHO-seeded FEL at nm wavelength D. Xiang March-17-2011

Introductions External seeding to improve temporal coherence of FEL output Success of ECHO relies on preservation of long-term memory of phase space correlations ECHO-7 to verify basic physics Before applying the ECHO technique to a user facility at ultrahigh harmonic number (100~200), it should be tested at a moderate harmonic number (25~50) to prove technologies and identify possible risks. SLAC provides an excellent base and offer much of the required infrastructure for the R&D Topic is to design a ~2 GeV ECHO-seeded FEL at SLAC

Time tables 03-2011, Fix basic beam parameters (energy, current, energy spread) and laser parameters 05-2011, Design of the photoinjector, linac, bunch compressors, undulators 07-2011, S2E simulation from cathode to undulator 09-2011, Time-dependent simulation for the ECHO-seeded FEL at nm wavelength Deliverables: a design report should be documented for SLAC-PUB.

Tentative parameters Seed laser wavelength: 258 nm (tripled from a Ti:Sapphire laser, the same as LCLS cathode laser) Target FEL wavelength: 10.32 nm (25th) / 5.16 nm (50th) Undulator period: 3 cm (LCLS-I) Beam energy: 1.64 GeV If we start from a 774 nm seed laser, the harmonic number is 75th and 150th accordingly

Open questions Coherent radiation, or FEL lasing? How many BCs? At what energy? 20 pC, 250 pC, 1 nC? Laser heater? Where to put the ECHO beam line? Compatible to FAULT? High harmonic number or short wavelength?