Development of a bellows chamber with a comb-type RF shield for high-current accelerators

An all-metal bellows chamber with a comb-type Radio Frequency (RF) shield for a high-current accelerator was developed and tested at the KEK B-factory (KEKB). The comb-type RF shield has no thin fingers but has nested comb teeth instead at an inner surface. The comb-type RF-shield has a higher thermal strength structurally compared to the conventional finger-type one. Leakage of the TE mode like HOM through the RF shield is almost suppressed. Two test models of bellows chambers installed in the 3.5 GeV positron ring of KEKB showed good properties up to a stored beam current of 1.5 A. The temperature rise of the corrugation was about 7°C and the temperature rise was about 16 of that of the bellows chamber with a conventional finger-type RF shield located under the same condition. The temperature rise of the comb teeth was about 22°C, while that of fingers of the finger-type RF shield was estimated to be about 105°C for the equivalent HOM power. No vacuum arcing was detected during beam operation.