Dynamic pressure in the high-power beam operation at J-PARC RCS

Kamiya, Junichiro   ; Yamamoto, Kazami   ; Takano, Kazuhiro; Kotoku, Hirofumi; Wada, Kaoru*; Yanagibashi, Toru*; Kurosawa, Shunta*

The vacuum system in the rapid cycling synchrotron of Japan Proton Accelerator Research Complex was constructed based on the design concept considering the effect of a dynamic pressure caused by a high-power proton beam operation. However, the high-power beam operation clearly has more effects than expected at the time of the design. The dynamic pressure with the beamline pressure runaway characterized by an extreme pressure rise of more than orders of magnitude occurred during beam operation. A systematic data observation showed that the pressure rise mechanism is a result of the gas desorption from the wall triggered by the hitting of the residual gas molecules ionized by the proton beam. The numerical calculation based on that model well reproduced the measured dynamic pressure behaviors in the beam operation. The calculation also showed that a large pumping speed and a small surface density of the adsorbed molecules are required to suppress the pressure runaway.