New 357 MHz Sub Harmonic Buncher

Abstract

KEK-ATF is doing R&D establishing high-current and low-emittance electron beam for the future linear colliders. In ATF, 15 ps length electron beam is generated by combination of a thermionic gun, a couple of 357 MHz SHBs, and a S-band TW buncher. In the linac, beam instability caused by the fluctuated amplitude and phase of SHBs has been observed. The reason of the fluctuation is considered to be the multi-pacting in the SHB cavity. In addition, Q value of the cavity is almost half of the designed value, then SHBs are not operated in an optimum condition. We have fabricated new SHBs with considerations avoiding the multi-pacting and recovering Q value. A simulation shows that bunching quality is improved with the new SHB cavity.