Feed RF Gun Design for the LCLS

In order to remove the dipole field introduced by the coupler in existing S-band BNL/SLAC/UCLA 1.6 cell RF gun, a dual feed design for the LCLS RF gun is proposed together with several significant changes. The improvements include adopting z-coupling instead of θ-coupling, modifying the iris dimensions and profile to increase 0- and π-mode separation from 3.4 to 15MHz and reduce the surface field on the iris, incorporating racetrack cavity shape to minimize the quadrupole field, increasing cooling for operation at 120Hz and other small changes to improve performance and diagnostic capabilities. The 3D gun structure had been modelled with the parallel finite element complex eigensolver Omega3p to provide the desired RF parameters and to generate the gun cavity dimensions needed for fabrication. In this paper the RF gun design will be presente