A high-DC-voltage GaAs photoemission gun: Transverse emittance and momentum spread measurements

We have built a high-DC-voltage photoemission gun and a diagnostic beamline permitting us to measure rms transverse emittance (/spl epsi//spl tilde//sub x/) and rms momentum spread (/spl delta/) of short-duration electron pulses produced by illuminating the cathode with light from a mode-locked, frequency-doubled Nd:YLF laser. The electron gun is a GaAs photocathode source designed to operate at 500 kV. We have measured /spl epsi//spl tilde//sub x/ and /spl delta/ for conditions ranging from emittance-dominated to space-charge-dominated. We report these measurements as functions of microbunch charge for different beam radii, pulse lengths, and voltages/field gradients at the cathode, and compare them with PARMELA calculations.