An Influence of ring-collimator malfunction on beam loss localization in the J-PARC RCS

Yoshimoto, Masahiro  ; Takeda, Osamu; Harada, Hiroyuki  ; Yamamoto, Kazami   ; Kinsho, Michikazu  

In the 3 GeV Rapid Cycling Synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC), a beam collimation system which aims to localize the beam loss at the collimators and to reduce the level of residual doses at the other devices is installed in the ring to achieve a 1MW high power beam operation. However vacuum leakage due to the collimator trouble occurred in April, 2016. Therefore an absorber No.5 in the collimation system had to be removed from the ring. Before resuming the beam operation, a new beam loss situation was simulated by using the particle tracking code. In the beam tuning, the transition of the beam loss distribution was measured by the beam loss monitors. We verified that the new beam situation was permissible, and the beam operation can be resumed. By following-up the transition of the residual dose distribution along the ring, the detailed beam loss structure can be understood. In this presentation, we report an influence of ring-collimator malfunction on beam loss localization in the J-PARC RCS.