High-voltage microwave-triggered switches

The operation of three types of experimental high voltage microwave-triggered switches developed by the University of St. Andrews and DRA Malvern is described. The POLOTRON and the microwave-triggered three-gap-switch (MTGS) are closing switches and the microwave-triggered tacitron, (MITTON) is a closing and opening switch. The switches are robust hydrogen thyratron type devices, with an annular geometry, where closure is achieved using microwave fields to ionize the low pressure gas within the switch. In the case of the MITTON, the switch is opened by the application of a negative bias voltage to a large area metal grid. The POLOTRON is designed for fast switching applications. Its annular geometry results in an inherent low inductance and anode fall-times of less than 3 ns have been measured for a cold-cathode POLOTRON at charging voltages up to 30 kV. The MTGS, also a cold cathode switch, was developed for use in the DUOTRON transient generator (a voltage doubler). Output voltages of up to 16 kV have been measured at repetition rates of 90 Hz. The MITTON has closing characteristics similar to the POLOTRON and anode voltage fall-times of less than 10 ns have been measured at voltages up to 16 kV. Opening times of 0.5 μs have been achieved with an anode voltage of 10 kV and current of 10 A