Repair and improvement of the J-PARC MR BPMS

The beam intensity is steadily increasing after the great earthquake in Mar. 2011. The recent Main Ring (MR) beam power at the RUN49 exceeded 230 kW. The earthquake had stopped all the J-PARC facility. The relay switches in the BPM (beam position monitor) circuits without the air conditioner suffered from contact-conductor contamination. It resulted in bad connection of the switches. Those relays were replaced in the 2012 summer shutdown. In addition for higher intensity beams, signal attenuators with the switchable LPF were attached just before the BPMC (a processing circuit for the BPM). The linearity, frequency response and temperature dependence were satisfactory. Before and after the repair and improvement, BPM offsets have been measured. The position resolutions were also measured with the three-BPM method. The results are between a few 10 μm ∼ a few 100 μm in rms, which varies with the beam intensity, BPM location and the BPMC setting as attenuation and gain. (author)