Numerical simulation of streamer–cathode interaction

Abstract

A self‐consistent fluid model has been used to analyze streamer arrival at the cathode and its transformation to the stationary cathode fall in a positive point–to–plane corona discharge in N₂ at 26.7 kPa. The model is based on a description of the electron and the ion kinetics by one‐dimensional continuity equations coupled with Poisson’s equation. The ions and electrons are assumed to be limited to a cylindrical channel with fixed radius and the field is computed using the method of disks. The computed current induced by the streamer–cathode interaction with a small cathode probe is compared with that measured experimentally. The cathode probe signal consists of an initial sharp current spike due to the displacement current followed, some 20 ns later, by a lower current hump due to the ion arrival at the cathode. The current signal is relatively insensitive to changes in the secondary electron emission coefficients. The results obtained indicate that the intense ionization and associated light flash experimentally observed near the cathode at the streamer arrival are not, as generally accepted, due to an intense electron emission but due to a sudden increase in the multiplication factor and a release of electrostatic energy accumulated in the streamer channel–cathode system.