R&D works on 1MHz power modulator for induction synchrotron

A proof of principle experiment of an Induction Synchrotron is scheduled in 2003 at the KEK 12GeV-PS. Proton bunches are accelerated with a 10kV of rectangular shaped induction voltage. An accelerating system consists of four induction cavities capable of individually generating a 2.5kV of output voltage. Each cavity is driven by a solid-state power modulator, which is operated at a revolution frequency of 600-800 kHz. The modulator circuit consists of MOS-FETs as switching element. Uniformity in the voltage waveform is crucial for the stable acceleration. Ringing in the voltage waveform caused by coupling of self-inductance of circuit and output capacitance of MOS-FETs deteriorates the uniformity. With the help of circuit analysis and simulation method of minimizing the self-inductance has been developed. Ratio of numbers of MOS-FETs in series and in parallel which defines the total output capacitance is also important to design the power modulator circuit. Power loss in MOS-FET is also important for stable operation of the power modulator. By the circuit analysis, it is also found that the output capacitance contributes to the power loss.