Transition of predominant mechanism for the deviation of micro-gap dc gas breakdown character with electrode gap changing

This paper explores the predominant mechanisms for the deviation of micro-gap dc gas breakdown and the transition between different mechanisms as the electrode separation d changing under a pin-to-plate electrode configuration using 2d3v particle-in-cell simulation with Monte Carlo collisions. The deviated breakdown characteristic curves as a function of d or gas pressure p are investigated and both present a plateau region. Through researching the position of discharge path, it is found that a self-modulation effect manages to maintain the breakdown voltage at the minimum value defined by Paschen’s curve in a certain d or p range and forms the plateau. The ranges of d and p for the plateau are also established. Theoretical calculation on the secondary electron emission coefficient induced by ion-enhanced field and determined by a surface roughness factor confirms that the ion-enhanced field emission effect affects the breakdown voltage significantly when d is below a critical value. The smaller the surface roughness factor is, the smaller the critical d will be. Under this effect, the breakdown voltage is decreased with d decreasing (also referred to as an increasing left branch with d increasing). Conclusively, the deviation characters of micro-gap gas breakdown are controlled by different mechanisms at different d ranges. The predominant mechanism for the deviation is the self-modulation effect, serving as the main reason for the plateau region, at moderate d of several micrometers and will transit to the ion-enhanced field emission effect, which is responsible for the increasing left branch at smaller d.