Improvement of an S-band RF-Gun cavity with a CS-TE photo-cathode

A 1.6 cell S-band photo-cathode RF-Gun is one of the good alternatives of the short pulse electron source. Therefore, we are operating as a high brightness short pulse electron source for studying a reaction of radiation chemistry [1], an inverse Compton scattering at Waseda University [2] and as an injector at KEK-ATF. To improve an electron beam quality and reduce a dark current, our group decided to improve the RF-Gun cavity. The resonance frequency tuning of the half cell of existing RF-Gun was performed by the torque control of Helicoflex seal on the cathode plate and two moving rod type tuners with a tuning hole were installed on the full cell. Newly designed RF-Gun cavity has four compact tuners on each cell, which can be tune the frequency to deform the cavity wall, to remove the Helicoflex seal and tuning holes that were considered to be the major cause of electric discharge and/or dark current source [3]. According to these improvements, the Q-value and shunt impedance of the cavity is 20% larger than that of existing guns. As the result, the reduction of dark current is demonstarated and the beam energy is reached up to 5.5MeV at 10MW RF input.