Optical diagnosis of vacuum breakdown characteristics under microsecond pulse

An optical diagnostic system to investigate the vacuum breakdown under microsecond pulsed voltage is constructed, which consists of a vacuum breakdown chamber of a high-voltage pulse driver and a high speed camera system. The jitter of the breakdown time delay is on the range of microsecond. To determine the moment of exposure, the gate-monitor output is compared with discharge current measured by a Rogowski coil. A Tesla type pulse driver delivers voltage pulses on the 2–2.5cm vacuum gap with a duration of 20–25 µs and an amplitude of 0–800kV. The electrodes are made of TC4 titanium alloy. The gap photos are obtained in each period of vacuum discharge, which show that: the plasma is formed initially on the cathode surface; the anode plasma is formed in several hundred nanoseconds due to the bombardment of electron-beam; the plasma expands with the development of breakdown until it extincts, and the average horizontal and vertical velocities of cathode plasma are 1.8 cm/µs and 4.2 cm/µs, respectively. Based on the results, a model of space-charge-limited electron current emitted from the cathode plasma is built to simulate the gap voltage and current. The simulation results correspond to the experimental counterparts.