FABRICATION AND PERFORMANCE TEST OF THE CAVITY BPM FOR KEK ATF2 AND PAL XFEL

A high-resolution beam position monitor (BPM) based on a pill-box type microwave cavity has been developed for the accurate beam position measurement in the KEKATF2. Based on the prototype cavity BPM designed in the KEK, the cavity structure and the isolation between horizontal and vertical modes are further improved by the collaboration between KEK, SLAC and PAL. The resonant frequency of the cavity and the isolation between horizontal and vertical modes can be tuned efficiently using tuning pins brazed on the cavity rim instead of the conventional tuning plunger. Offset between electrical and mechanical centers could be reduced by tuning within +/- 5 um, the isolation tuned better than 50 dB, and the 100 nm resolution of the cavity BPM has been proved through the beam tests in the ATF extraction beamline. Technical design considerations, fabrication, and test results of the cavity BPM are described in this paper.