Electron Beam and Rf Characterization of a High- Brightness X-band Photoinjector

We report detailed experimental results on an X-band (8.547 GHz) rf photoinjector, currently being commissioned at UC Davis on the LLNL site. The device operates with an average accelerating gradient in the 50100 MeV/m range, and produces relativistic (1.5-2 MeV) photoelectron bunches, with a measured relative energy spread < 1.8%, at the resolution limit of our energy spectrometer. The measured quantum efficiency is 2×10, at the maximum of the Schottky curve, and the 90% normalized emittance is measured at 1.65 π–mm mrad for 20 pC of charge. The bunch duration is extremely short, under the 700 fs resolution of our streak camera. Timing jitter has also been measured directly from the delay between the UV light diffused by the photocathode, and systematic delay is found, corresponding to the time-offlight difference between the UV photons and the accelerated electrons, and the additional timing jitter is estimated at 5 ps, or 15 degrees of rf phase. Finally, coherent synchrotron experiments are underway, as the photoelectron bunches radiate coherently up to the THz region.