RF characterization of a tunable, high-gradient, X-band photoinjector

Highly accurate measurements of an X-band (8.538 GHz) radio frequency (RF) gun, designed to produce short (<1 ps), relativistic (5 MeV), low-emittance (<1 pi -mm/mrad, at 0.1 nC) electron bunches, have been performed at medium-power levels (1 kW, 6 mus, 30 Hz). Balanced (within 3%), high-Q (4274), pi -mode excitation at critical coupling(S-11 < -80 dB) has been demonstrated by performing in situ phase measurements. A new tuning method to accurately adjust the coupling has been successfully implemented, which complements the independent tuning of the half and full cells, and the precise (-136 kHz/<degrees>C) temperature tuning of the gun. Finally, preliminary photoelectron results are also outlined.