Critical Parameters of Electron Avalanches in Air in Strong Homogeneous Fields.

A mathematical model of electron avalanches and avalanche–streamer transitions in air is presented that is based on the drift–diffusion model of discharges and takes into account the drift of electrons in an electric field, impact ionization of molecules by electrons, and their adhesion and detachment. The transition criterion is the appearance of a quasi-neutral plasma channel between the avalanche and its wake. An estimate is given of the critical number of electrons and the minimum tension between the avalanche and its wake at the moment of the avalanche transformation into a streamer in air under normal atmospheric conditions. Discharges were studied in intervals of 0.1–0.5-cm length with a homogeneous field with an intensity of (5–8) × 10⁴ V/cm. It is shown that the critical number of electrons weakly depends on the value of the intensity and is in the range of (3.9–5.5) × 10⁷. The stability of the applied mathematical model to changes in its parameters and the correspondence of the calculation results in confirmation of the known patterns of development of avalanches and avalanche–streamer transitions. [ABSTRACT FROM AUTHOR]