Present Status of J-PARC Ring RF Systems

The accelerator of the J-PARC complex consists of the 400MeV (initially 181MeV) linac, the rapid cycling 3GeV Synchrotron and the 50GeV main Synchrotron. To accelerate an ultra-high intense proton beam, the synchrotrons require a high field gradient RF system (∼ 25kV/m). Alleviating space charge effects is a key issue for minimizing beam losses during a cycle. Longitudinal bunch manipulation is also considered as well as acceleration. Magnetic alloy loaded cavities are the most practical choice for the J-PARC. Such system provides high field gradient, and broadband behaviour. It is a stable passive system without tuning control. Multi-tone signals can be fed into the same cavity for acceleration and bunch manipulation. However, the harmonics of circulating beam current within the cavity bandwidth must be taken into account. A feed-forward scheme is used for compensating beam-induced voltages. The low level RF system is fully digital to provide precise control. The specification is based on high reliability and reproductivity. The design consideration of the whole RF system will be described and the current status presented.