Performance of a very high voltage photoemission electron gun for a high brightness, high average current erl injector

We have constructed a very high voltage DC photoemission electron gun as the electron source of an injector for an Energy Recovery Linac (ERL) based synchrotron radiation light source. The gun is designed to deliver 100 mA average beam current in a 1300 MHz CW bunch train (77 pC/bunch), and to operate up to 750 kV cathode potential. Negative electron affinity (NEA) photocathodes are used for their small thermal emittance and high quantum efficiency. A load-lock system allows introduction, cleaning, and activation of cathodes outside of the electron gun. Cathodes are cleaned by heating and exposure to atomic hydrogen, and activated with cesium and nitrogen trifluoride. Cathode electrodes of 316 LN stainless and Ti4V6Al have been used with a beryllium anode. The internal surface of the ceramic insulator has a high resistivity fired coating, providing a charge drainage path. Non-evaporable getter (NEG) pumps provide a very high pumping speed for hydrogen. Operating experience with this gun will be presented.