A photocathode RF gun design for a mm-wave linac-based FEL

In recent years, advances in the RF gun technology have made it possible to produce small beam emittances suitable for short period microundulators which take advantage of the low emittance beam to reduce the wavelength of free-electron lasers (FELs). At the Advanced Photon Source, we are studying the design of a compact 50-MeV superconducting mm-wave linac-based FEL for the production of short wavelengths (~300 nm) to carry out FEL demonstration experiments. The electron source considered for the linac is a 30-GHz, 3½-cell π-mode photocathode RF gun. For cold model RF measurements a 15-GHz prototype structure was fabricated. Here we report on the design, numerical modeling and the initial cold-model RF measurement results on the 15-GHz prototype structure