Microbubble-Based Model Analysis of Liquid Breakdown Initiation by a Submicrosecond Pulse

An electrical breakdown model for liquids in response to a submicrosecond(∼100ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the prebreakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and observed optical emission

A new design concept for field distortion trigger spark gaps

A common field distortion triggered spark gap utilizing geometric field enhancement at sharp edges usually operates in a cascade mode via the trigger electrode. A new trigger concept is proposed allowing strong field enhancement and direct breakdown between the two main electrodes. A test setup was designed to prove the feasibility of this concept. Experimental results on delay and jitter depending on percent breakdown voltage are presented. Best results achieved are a delay of 9 ns and a jitter of 2 ns at a self-breakdown voltage of 15 kV

Effect of Dielectric Photoemission on Surface Breakdown: An LDRD Report

The research discussed in this report was conceived during our earlier attempts to simulate breakdown across a dielectric surface using a Monte Carlo approach. While cataloguing the various ways that a dielectric surface could affect the breakdown process, we found that one obvious effect--photoemission from the surface--had been ignored. Initially, we felt that inclusion of this effect could have a major impact on how an ionization front propagates across a surface because of the following argument chain: (1) The photon energy required to release electrons from a surface via photoemission is less than the photon energy required to ionize gas molecules directly. (2) The mean free path of a photon in gas is longer for low-energy photons than for high-energy photons. (3) Photoionization is a major effect in advancing the ionization front for breakdown in gas without a surface, therefore, we know that even high-energy photons can be released from the head of a streamer and propagate some distance through the gas. Our hypothesis, therefore, was that photons with energies near the threshold of photoemission could travel further in front of the streamer before being absorbed than higher-energy photons needed for photoionization, yet the lower-energy photons, with the help of the surface, could still create seed electrons for new avalanches. Thus, the streamer would advance more rapidly next to a surface than in gas alone. Additionally, the photoemission from the surface would add to the electrons in the avalanche and cause the avalanche to grow faster. After some study, however, we are forced to conclude that although photoemission does contribute to avalanche growth at fields near breakdown threshold, secondary electron emission causes electrons to stick to the surface and cancels out the growth due to photoemission. This conclusion assumes a discharge that occurs over a short period of time so that charging of the surface, which could alter its secondary electron emission characteristics, does not occur. This report documents the numerical work we did on investigating this effect and the experimental work we did on pre-breakdown phenomena in gas