Prospects for high power linac coherent light source (LCLS) development in the 1000 Å−1 Å wavelength range

Electron bunch requirements for single‐pass saturation of a Free‐Electron Laser (FEL) operating at full transverse coherence in the Self‐Amplified Spontaneous Emission (SASE) mode include: 1) a high peak current, 2) a sufficiently low relative energy spread, and 3) a transverse emittance e[r‐m] satisfying the condition e≤λ/4π, where λ[m] is the output wavelength of the FEL. In the insertion device that induces the coherent amplification, the prepared electron bunch must be kept on a trajector sufficiently collinear with the amplified photons without significant dilution of its transverse density. In this paper we discuss a Linac Coherent Light Source (LCLS) based on a high energy accelerator such as, e.g., the 3 km S‐band structure at the Stanford Linear Accelerator Center (SLAC), followed by a long high‐precision undulator with superimposed quadrupole (FODO) focusing, to fulfill the given requirements for SASE operation in the 1000 A−1 A range. The electron source for the linac, an RF gun with a laser‐ex...