Performance of multi-harmonic RF feedforward system for beam loading compensation in the J-PARC RCS

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

The beam loading compensation is a key part for acceleration of high intensity proton beams in the J-PARC RCS. In the wide-band MA-loaded RF cavity, the wake voltage consists of not only the accelerating harmonic component but also the higher harmonics. The higher harmonic components cause the RF bucket distortion. We employ the RF feedforward method to compensate the multi-harmonic beam loading. The full-digital feedforward system is developed, which compensates the first three harmonic components of the beam loading. We present the results of the beam test with a high intensity proton beam ( ppp). The impedance seen by the beam is greatly reduced, the impedance of the fundamental accelerating harmonic is reduced to less than 25 in a full accelerating cycle, while the shunt resistance of the cavity is in the order of 800 . The performance of the feedforward system is promising for achievement of the design beam power, 1 MW, in the future.