Multi-harmonic RF control system for J-PARC RCS

The RF cavity of J-PARC Rapid Cycling Synchrotron (RCS) has a low Q value and a wide band which covers the frequency from the accelerating frequency to the second harmonic frequency. The cavity is driven by a composite signal of the fundamental RF and the second harmonic RF. The system acts as a bunch shaping system as well as an accelerating system. In this presentation, a multi-harmonic RF control system is studied. The signal processing is based on a combination of digital hardware like 16 bit multipliers, arithmetic units, and FPGAs with commercially available signal processors. The beam loading compensation is a critical issue because of the high beam-current in the ring. The RF feedforward compensation system is discussed. Also the stability is discussed under the beam feedback loops.