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Report No.

Cavity voltage variation at beam extraction in the J-PARC MR

Tamura, Fumihiko  ; Yoshii, Masahito*; Omori, Chihiro*; Yamamoto, Masanobu  ; Nomura, Masahiro ; Shimada, Taihei ; Hasegawa, Katsushi*; Hara, Keigo*

J-PARC MR provides high intensity proton beams of 390 kW to the neutrino experiment. The proton beams are extracted by fast extraction. It has been found that the cavity voltage goes up for about 20 $$mu$$s just after extraction. It is because the rf feed forward system for beam loading compensation outputs compensation signals for its system delay. The MR cavity has a relatively low Q value of 22 and the cavity voltage can varies in the order of 10 $$mu$$s. The voltage variation of the cavity voltage increases with the beam intensity and it is a possible reason of the damage of the gap capacitors. A counter measure using the inhibit function of the summation amplifier in the LLRF system has been applied. In this presentation, we present the details of the cavity voltage variation and the results of the counter measure. Also, we present the analysis of beam loading using the voltage variation.



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