Upgrade of the ring collimator at the J-PARC RCS

Okabe, Kota  ; Kamiya, Junichiro   ; Moriya, Katsuhiro  ; Shobuda, Yoshihiro   ; Takahashi, Hiroki  ; Takayanagi, Tomohiro   ; Yoshimoto, Masahiro  ; Yamamoto, Masanobu   ; Yamamoto, Kazami   

The Japan Proton Accelerator Research Complex 3-GeV rapid cycle synchrotron (RCS) has a collimator to prevent radioactivation of accelerator devices. This collimator has several absorber parts composed of copper blocks to prevent large amplitude beam particle oscillations. In the RCS, this collimator was performed from the beginning of beam operation in 2007. However, in April 2016, Absorber Unit 5 of the collimator absorber broke down, and a large vacuum leak occurred. As a result, long-term restoration work was required. We first disassembled the broken absorber unit, which had high radiation from the beamline, and investigated the cause of the accident. It was found that the absorber blocks collided with each other due to moving beyond the designed drive range. The newly developed absorber can be driven over a broader range than conventional absorbers, absorbing scattered proton beams more efficiently. However, in the checking process of a new collimator operation, other new problems emerged. The problem was damage to the absorber block due to the RF contacts placed between the block and the chamber to suppress beam instability. We confirmed no significant problems, such as beam instability, even if the RF contacts were removed. To create an absorber that can operate stably for an extended period with a low possibility of severe failure of highly radioactive parts.