NEUTRAL HEATING IN GLOW TO SPARK TRANSITION IN AIR AND NITROGEN

The heating of the neutral molecules in the glow to spark transition in air and nitrogen has been theoretically studied. A hydrodynamic first-order model has been used for electrons (density, momentum) and a second-order model (density, momentum, temperature) for neutral molecules. The interaction between the electron dynamics and the neutral dynamics has been compared in two kinds of discharges: a fast discharge (170 ns) in an overvolted plane parallel gap in nitrogen, and a discharge of long duration (1. 15 mu s) in a positive point-to-plane gap in air. The gas heating gives rise to a neutral depopulation in the core of the discharge. This leads to an increase of the reduced electric field E/N, thus to an increase of the electron production and thus of the current. In this kind of discharge, the heterogeneity of the neutral gas leads to the breakdown, owing to a constriction of the current core induced by the depopulation mechanisms.