High power water switches: postbreakdown phenomena and dielectric recovery

The physical processes following the electrical breakdown of water between planar and hemispherical electrodes separated by a sub-millimeter gap have been studied using electrical and optical diagnostics. The expanding plasma column after breakdown generates first shockwaves and at a later stage a vapor bubble which expands for about 200 μs and then decays with a time constant of I ms. The bubble decay time determines the dielectric recovery of the switch as has been shown with pulse-probe experiments.