The new BPMs for the J-PARC 350BT optics measurements at high radiation fields

In order to investigate the optics parameters of the 3 GeV RCS to 50 GeV MR Beam Transport (350BT) in detail, we have installed 3 Beam Position Monitors (BPMs) additionally in the gap of the quadrupole magnets QFS1, QFS2, QFS3 in the collimator area of the 350BT. The old BPMs are the electro-static type BPM, however, as for the new BPMs, the magnetic loop coupling type BPM were adopted to diminish pseud signals from the induced charge on the signal pick-up electrodes; some of the scattered primary and generated secondly charged particles from the collimators can go directly into electrodes and generate charges. The details of the new BPMs are described in this paper with the estimated position resolutions using the 3-BPM method. (author)