Measurement of residual dose distribution and activation due to beam losses in J-PARC RCS

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

Suppression of device radiations due to beam losses in the high intensity proton accelerators is one of the key issues to achieve MW class high power beam operation. In the J-PARC RCS, Ring collimator system which can localize the beam loss in the ring is adopted to suppress the device radiations. However, high residual doses are observed around the stripper foil. During the multi-turn charge exchange beam injection, not only the injecting beam but also circulating beam hit the foil, and then a large number of secondary particles, namely protons and neutrons, are generated. PHITS simulation results indicate that the secondary particles cause the high residual doses around the foil. Thus, we developed a new BLM which can detect the beam loss at the localized spot area. This new BLM can relate the beam loss with the radio activation of the device at the spot area. Detected radiations by this new BLM are occurred during the beam injection period and the total amount of the signal is directly proportional to the frequency of both the injecting and the circulating beam irradiation. Beam loss evaluation method combining the detailed residual dose survey by the GM counter after the beam stop into the radiations measurement by the BLM during the beam operation is effectively to reveal the beam losses structure from the point of view of the beam dynamics in the accelerator. In this presentation, we report the relation between the BLM signals and residual doses, and the beam losses structure and the mechanism.