Evaluating microgap breakdown mode transition with electric field non-uniformity

Abstract

This paper evaluates the transitions between the breakdown modes that are dominated by field emission (FE) and by secondary electron emission (SEE) in argon microgaps, based on a mathematical model originally proposed for the modified Paschen’s curve (Go and Pohlman 2010 J. Appl. Phys. 107 103303). In the present model, instead of assuming a constant electric field across the gap, the spatial distribution of the electric field due to the presence of a parabolic cathode protrusion is implemented, and a modification of the first Townsend ionization coefficient for microscale gaps from particle-in-cell/Monte Carlo collision simulations is employed (Venkattraman and Alexeenko 2012 Phys. Plasmas 19 123515). The breakdown mode transitions are quantified by the variations of gas pressure and gap distance. It is found that assuming a constant electric field across the gap will overestimate the electron avalanche, which underestimates the breakdown voltage and shifts the breakdown mode transitions to a smaller gap. By varying the field enhancement factor, the critical point of the breakdown mode transition can be significantly adjusted. Increasing the field enhancement factor will lower the breakdown voltage in the FE regime and increase the breakdown voltage in the SEE regime.