Evaluation of the frequency response of the RF gap voltage monitor of the J-PARC RCS

Okita, Hidefumi  ; Tamura, Fumihiko   ; Yamamoto, Masanobu   ; Nomura, Masahiro  ; Shimada, Taihei ; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; Sugiyama, Yasuyuki*; Furusawa, Masashi*

The J-PARC RCS employs the dual-harmonic operation, in which the fundamental and the second harmonic RF voltages are used for the beam acceleration. The each harmonic voltage and phase applied for the acceleration gaps are controlled by the multiharmonic vector RF voltage control system using the signal from the cavity gap voltage monitor equipped with the one of the acceleration gaps of the each RF cavity. Since the bunch shape varies depending on the relative phase of each harmonic, it is important to evaluate the frequency response of the cavity gap voltage monitor. The measurements of frequency response of the cavity gap voltage monitor and beam tracking simulation considering the measurement were carried out. As a result, it was confirmed that the bunch shape of the beam tracking simulation reproduces the one measured at the 1MW beam operation well. The details of the frequency response measurement, the beam tracking simulation and the discussion of the cavity gap voltage monitor circuit are reported.