Model analysis of self- and laser-triggered electrical breakdown of liquid water for pulsed-power applications

Electrical breakdown simulations for liquids, in response to a submicrosecond (∼100-200 ns) voltage pulse, are carried out. It is shown that breakdown is initiated by field emission at the interface of preexisting microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. The model used in this paper adequately explains experimentally the observations of prebreakdown current fluctuations, streamer propagation and branching, as well as disparities in hold-off voltage and breakdown initiation times between the anode and the cathode polarities. It is demonstrated that polarity effects basically arise from the large mobility difference between electrons and ions. Breakdown is shown to occur either through the application of an overvoltage pulse, or be triggered by an external laser under electrical stress. With laser excitation, a string of point plasma formation is predicted, followed by rapidly propagating streamers and subsequent breakdown. This matches the recent work at Sandia National Laboratories.