Current Increase at Constant Amplification Factor in Steady Corona with Coaxial Cylindrical Geometry

It has long been known that above onset of steady positive wire corona with coaxial cylindrical geometry, Townsend's relation of 1914 relating current i and over-voltage, V-Vg, of the form V-Vg=Bi/V applies over a considerable range. This law is deduced assuming a constant potential across a zone of limited constant ionizing radius. Such assumption implies a constant Townsend amplification factor for ionization by collision, a fact just recently experimentally established by Colli, Facchini, and Gatti. The corona current i on this theory, however, increases many times despite constant amplification factor. It is shown that this occurs by slight temporary raising of the amplification factor producing a rapid proliferation of ionizing sequences over the anode surface, increasing current and space charge density, but maintaining essentially constant amplification factor. This action has a bearing on the spread of the normal glow discharge over the cathode.