THE THEORY OF POSITIVE GLOW CORONA

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by sol ving the continuity equations for electrons, positive ions, negative i ons and metastable oxygen molecules, coupled with Poisson's equation. A series of 'saw-toothed' current pulses of period about 1 mu s is pre dicted with a DG current level. Accompanying the current peaks are dis crete pulses of light 30 ns wide. Successive 'shells' of positive ions , from successive current pulses, carry 96% of the mean current. The m ean current-voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negati ve ions by metastable oxygen molecules. Photo-ionization is crucial fo r the discharge at the anode and for the formation of negative ions th roughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility . The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and su b-microsecond voltage pulses are found to produce streamers. The resul ts for concentric-cylinder electrodes are described briefly.