High-power solid-state switch using static induction thyristors for the klystron modurator

We have developed a solid-state switch with static induction thyristors (SI-thyristors) for the klystron modulator of the L-band electron linac at the Institute of Scientific and Industrial Research, Osaka University. The switch is designed to meet the specifications that the maximum voltage is 25 kV and the maximum current is 5 kA at a repetition rate of 10 pps, so that it consists of six parallel and ten series circuits of 60 SI thyrsitors. The turn-on time of the switch is measured to be 270 ns. It is retrofitted in the modulator to generate 1.3 GHz RF pulses of the maximum peak power of 30 MW for a duration of 4 jis or 25 MW for 8 μs. The linac is successfully operated with the switch under the specified conditions, which demonstrates that it can be used as a high-power switch for the modulator. The pulse-to-pulse variation of the klystron voltage is measured to be 0.015% though it is close to the noise level of our measurement system. Variations of the RF power and the phase - as well as the variation of the klystron voltage measured with the solid state switch are significantly smaller than those obtained with a thyratron, and hence the stability of the main RF system is remarkably improved. The solid-state switch has been used in normal operation of the linac for one year or more than 2,000 hours without any serious troubles. Thus we have confirmed its robustness and long-term reliability.