Investigating Anode-Initiated High Voltage Vacuum Surface Flashover Common to Large-Scale Pulsed Power Systems

Anode-initiated high-voltage vacuum surface flashover is a prominent failure point in large-scale (megavolt and mega-ampere) pulsed power machines. To investigate the underlying basic mechanisms of anode-initiated vacuum surface flashover, a moderate-scale test platform was developed at the hundreds of kilovolt level to emulate the conditions in large-scale machines. This system comprises a positive 45-degree wedge of insulator placed between a hemispherical anode with a 2-cm radius and a planar cathode, approximating a normalized electric field profile found in large-scale pulsed power insulator stacks. An 8-stage Marx generator that produces a pulse up to 240 kV with a ~50 ns risetime is used to provide the high voltage excitation; experiments are conducted across 2 to 6 mm sized flashover gaps at a ~ 10
⁻⁶
Torr background pressure. This study reports the statistical characterization of high voltage vacuum surface flashover, high speed and time-integrated imaging of flashover development, and temporally resolved emission spectroscopy from 200 nm to 600 nm of self-produced light emanating from these flashover events. Future steps towards an upgraded experimental platform with 600 kV capability are discussed.