RF PROCESSING OF L-band RF gun for KEK-STF

Status of RF processing of L-band RF gun at KEK-STF (Superconducting Test Facility) is presented. A 1.3 GHz normal conducting RF photo-injector has been prepared for KEK-STF, where Super-conducting technology is being developed for ILC (International Linear Collider). MEXT Quantum Beam project, high brightness X-ray generation by inverse laser Compton scattering, also will be carried out at STF. In both cases, the high intensity electron beam in multi-bunch and long macro-pulse up to 0.9ms has important roles. The RF gun cavity has been fabricated by DESY-FNAL-KEK collaboration and the first high power RF processing has been carried out in 2009, but a large amount of dark-current (280μA at 28 MV/m) was observed. In order to cure the problem, the cavity surface was treated by ethanol rinsing to suppress the dark current. The second high power RF processing was performed in January 2011. The dark-current was decreased by an order of magnitude, down to 18μA at the same condition. For each processing, RF power was up to 1.7 MW, which was limited by the power source. The real operation will be made at 3.5 MW input power with a new power source. The third high power RF processing is scheduledwith this newpower source from September 2011.