Present status of the J-PARC MR BLM system

For the Main Ring synchrotron (MR) of J-PARC, two types BLMs that are the Proportional type Beam Loss Monitors (P-BLMs) and coaxial cable based Air Ionization ion-Chambers (AICs) have been installed, however, up to the present, only the P-BLMs are mainly used at a beam commissioning. The sensitivities of the P-BLMs against a beam loss have been tested, where the beam loss was controlled by shift bump orbit at some points, injection area, slow extraction line, fast extraction line, and 1st Arc. The sensitivities are varied depending on the loss points and show clear gain reduction. A part of the AICs will be on operation from next beam run started from this October. In this paper, the present status of the beam loss monitor system is presented. (author)