Multiharmonic RF feedforward system for beam loading compensation in wide-band cavities of a rapid cycling synchrotron

Tamura, Fumihiko   ; Yamamoto, Masanobu   ; Omori, Chihiro*; Schnase, A.; Yoshii, Masahito*; Nomura, Masahiro  ; Toda, Makoto*; Shimada, Taihei ; Hara, Keigo*; Hasegawa, Katsushi*

For the acceleration of very high intensity protons in the 3 GeV RCS of the J-PARC, the beam loading compensation in the rf accelerating cavities is implemented. The wake voltage in the wide-band MA cavity consists of not only a component of the fundamental accelerating rf, but also the higher harmonics. We developed a multi-harmonic feedforward compensation system, which handles the most important three harmonics ( = 2, 4, 6). The function of the multi-harmonic feedforward is described. Adjustments of the amplitude and phase patterns for the cancellation of the wake voltage during the acceleration period are not trivial. We developed the commissioning methodology of the feedforward. We describe the methodology in the cases without and with driving the accelerating rf. We describe the commissioning results and the beneficial effects of the feedforward compensation in the beam operation.