Use of an SCR switch for a long pulse high duty line type modulator

Abstract An SCR switch for a long pulse, high duty, line type modulator, which had been fabricated as a prototype for the development of an rf source for the JHP 1 GeV proton linac, has been constructed and tested. The switch was designed to be used for discharging a pulse-forming network charged at 40 kV and producing pulses with MW of peak power (20 kV × 750 A) and 450 kW of average power (15 MW × 600 μs × 50 pps). This switch comprises of 30 general use type SCRs, arranged in series so as to withstand high voltage. After installing this switch in the modulator as a replacement of the thyratron switch, a test was carried out up to 12.5 MW peak and 250 kW average output power, which was limited by the maximum capabilities of the present modulator (400 μs) and a klystron, used as a load through a pulse transformer (18.6 kV at primary, 130 kV at secondary). The design considerations and the test results of the SCR switch are described, along with an outline of the prototype modulator.