Mitigation of cavity voltage jump due to high intensity beam extraction in J-PARC RCS

Tamura, Fumihiko   ; Sugiyama, Yasuyuki*; Okita, Hidefumi  ; Yamamoto, Masanobu   ; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Nomura, Masahiro  ; Shimada, Taihei ; Hasegawa, Katsushi*; Hara, Keigo*; Miyakoshi, Ryosuke*; Adachi, Kyosuke  

The 3GeV RCS of J-PARC accelerates proton beams with a maximum beam intensity of 8e13 ppp, utilizing the features of magnetic alloy (MA) cavities. The beam is extracted in a single turn by kicker magnets, and immediately after the beam is extracted, a short voltage jump occurs in the cavity. This is due to a delay in the voltage control feedback, which takes a certain amount of time to respond to the step-like decrease of beam current upon single-turn extraction. In a wideband (Q=2) MA cavity, this response delay is observed as a voltage jump. This voltage jump can cause damage to the cavity system if the voltage at the time of extraction is high. Therefore, we prepared a logic to suppress the output synchronously with the beam extraction as a function of the LLRF control system. The details of the function and test results are reported.