A Low Emittance Injector for LCLS-II-HE

The SLAC High Energy upgrade of LCLS-II will double the beam energy to 8 GeV, increasing the XFEL photon energy reach to about 16 keV. The energy reach can be extended to 20 keV if the beam emittance can be halved, which requires a higher gradient electron gun with a lower intrinsic emittance photo-cathode. To this end, a superconducting RF (SRF) gun R&D program is being launched this year in which SLAC will partner with U.S. labs with SRF experience to build a gun prototype. The goal in the next three years is to demonstrate stable CW operation of the gun at a cathode gradient of at least a 30 MV/m, significantly higher than the 20 MV/m gradient that has been achieved to date in either normal-conducting or superconducting CW guns. In this talk, we will describe the design of a 100 MeV second injector beamline for LCLS-II-HE including the simulations and multi-object genetic algorithm (MOGA) optimizations that were performed using the LUME tools. Performance with different cathode gradients, bunch charges and bunch mean transverse energies (MTEs) will be presented.