Multiharmonic RF feedforward system for compensation of beam loading and periodic transient effects in magnetic-alloy cavities of a proton synchrotron

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

Beam loading compensation is a key for acceleration of a high intensity proton beam in the MR of J-PARC. Magnetic alloy loaded rf cavities with a Q value of 22 are used to achieve high accelerating voltages. The cavity is driven by a single harmonic (h = 9) rf signal while the cavity frequency response also covers the neighbor harmonics (h = 8, 10). Therefore the wake voltage induced by the high intensity beam consists of the three harmonics, h = 8, 9, 10. We employ the rf feedforward method to compensate the beam loading ofthese three harmonics (h = 8, 9, 10). The full-digital multiharmonic feedforward system was developed for the MR. The commissioning of the feedforward system has been performed by using high intensity beams with 1.010 protons per pulse. The longitudinal oscillations due to the beam loading are reduced. By the beam loading compensation, stable high power beam operation is achieved.