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We present a design for a compact FEL source of ultra-fast, high-peak flux, soft x-ray pulses employing a high-current, GeV-energy electron beam from the existing laser-plasma accelerator at LBNL's LOASIS facility. The proposed ultra-fast source would be intrinsically temporally synchronized to the drive laser pulse, enabling pump-probe studies in ultra-fast science with pulse lengths of ~10–25 fs. Owing both to the high current (>10 kA) and reasonable charge/pulse (~0.1-0.5 nC) of the laser-plasma-accelerated electron beams, saturated output fluxes are potentially on the order of 1014 photons/pulse. We examine devices based both on SASE and high-harmonic generated input seeds to give improved coherence and reduced undulator length, presenting both analytic scalings and numerical simulation results for expected FEL performance. A successful source would result in a new class of compact laser-driven FELs in which a conventional RF accelerator is replaced by a GeV-class laser-plasma accelerator whose active acceleration region is only several cm in length.
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