Abstract
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.
Highlights
For past decades, the breakdown character of dc gas discharge under micron or sub-micron electrode separations has drawn extensive attention and exhibits its significance mainly in two communities
With d decreasing from the critical value, the ion-enhanced field emission effect starts to develop and gets stronger quickly, resulting in the breakdown voltage decreasing further from the plateau and the deviated left branch, which has been well studied theoretically and experimentally
Without the ion-enhanced field emission factor introduced in simulation, the deviation of a plateau region is observed in the Vbr–d curves, which is consistent with the previous experimental results, and in the Vbr–p curves, illustrating that the ionenhanced field emission effect is not the reason for the plateau region
Summary
The breakdown character of dc gas discharge under micron or sub-micron electrode separations has drawn extensive attention and exhibits its significance mainly in two communities. The breakdown characteristic curve of gas discharge under electrodes with remarkable curved surfaces, for example a pinto-plate or pin-to-pin electrode configuration, is usually characterized by an increasing left branch at very small d, a plateau branch at moderate d, and a further increasing right branch at larger d. The former two branches are generally lower than the breakdown voltage predicted by Paschen’s law. Electrodes of other geometric configurations with curved surfaces are employed to conduct the related research and similar results are obtained.
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