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

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.

The effect of micro-gap discharge paths on ionization coefficients and similarity theory

“…Resulting in the product of gas pressure and the discharge path length(ps) approximates the pd value associated with the minimum breakdown voltage, thus sustaining the minimum breakdown voltage [24,25].…”

Breakdown characteristics in dielectric-confined microcavity discharge of plate electrodes

“…However, microscale geometries present a challenge to the traditional understanding of the electrical breakdown of a gas gap that has described and predicted for over a century by Paschen's law [6], which shows that the breakdown voltage V br as a function of the product of gas pressure p and gap distance d (also known as a Paschen curve) has a decreasing left branch and an increasing right branch. In the case of micro-gap discharge, the gas breakdown features deviate significantly from the classical Paschen's law when the dimensions are in the range of 1-10 µm [1] due to the distribution of an ion-enhanced field emission effect [7] or the self-modulation effect [8]. This paper focuses on microcavity discharge.…”

Effect of Breakdown Path on Discharge of Micro-Gap Electrode

“…In a small air gap, the self-modulation effect of the electron makes the discharge path longer [11], making the PD value approximately equal to the Pd value corresponding to the minimum breakdown voltage, that is, PD ≈ (Pd) min (D is the actual breakdown path distance). By establishing a DCP model of two non-parallel straight plate electrodes, Yu Bo and other scholars found that when the pressure changes, the initial path of breakdown will shift [12], and the entire electrode channel will always choose the path most likely to cause breakdown under different working conditions. At present, based on the breakdown characteristics of the at electrode with micron spacing and the appearance of the breakdown voltage "plateau period", Paschen curve is no longer fully applicable to the breakdown characteristics of the at electrode.…”