Nanosecond pulser thyratrons

A thyratron is constructed capable of meeting the Type II requirements for voltage, peak current and average power, and has characterized its resistive fall time, recovery time, and forward voltage holdoff as functions of pressure and triggering configuration. A low inductance circuit has been built, incorporating the thyratron, a 5 nF fast discharge capacitor, and a 60 pF capacitor to simulate the loading effect of a magnetron or EIO. A theoretical model for the circuit which includes the effects of thyratron resistance (time varying), and inductance was developed. The resistive fall time decreases with rising pressure, but more slowly than predicted by gas breakdown theory, suggesting that it is being limited by the internal design of the thyratron. Fall times of only around 3 ns are obtainable before the pressure gets too high, (0.9 torr), for the 50 microns s recovery time required for 20 kHz operation. This will necessitate experimentation with ferrites to delay the current rise until the anode fall is over. Electrode design modifications to decrease the fall and recovery times will also be tested. The 6 kv forward holdoff required under Type II conditions has been attained at pressures up to 1.3 torr by use of a fast pulse charging.