Particle-in-cell simulations of the direct-current argon breakdown process in the 10–300 kV range

Abstract

Direct-current ionization breakdown in argon at very high voltage on the low-pressure branch of the Paschen curve is studied by means of kinetic simulation. The employed particle-in-cell/Monte Carlo collision model tracks the motion of electrons, ions and fast neutral atoms, as well as their collisions with the background gas. Secondary electron emission due to the bombardment by ions and fast atoms, as well as backscattering of different species on the electrode surfaces are also consistently accounted for. To validate the model, we compare the Paschen curve predicted by kinetic simulations against published experimental results as well against the prediction of a reduced (fluid) model. The model is then applied to predict, for the first time, the low-pressure branch of the Paschen curve for argon gas in the 10–300 kiloVolt range of applied voltage. One of the findings is the existence of a turning point on the Paschen curve at and , where is the breakdown voltage and the reduced pressure is the product of the gas pressure with the inter-electrode distance. According to our analysis, the presence of the turning point is due to the phenomena of electron and ion runaway in high electric field. We further investigate the role of the heavy species (i.e. ions and fast neutral atoms) in sustaining the Townsend discharge at high voltage and thus setting the breakdown threshold. Specifically, the role of fast atoms is significant over the entire low-pressure branch of the Paschen curve due to their contribution to both ionization and secondary electron emission. Also, the ions, as the precursor for the fast atoms, show an important influence on the latter process. The newly predicted low-pressure branch of the Paschen curve for argon at high voltage should provide an essential reference for the design of high-voltage devices, e.g. circuit breakers in electrical power transmission.