The Growth of Corona Discharges in Air

Abstract

The various stages of growth of corona discharges in a point-to-point gap were photographed in a cloud chamber. The gas investigated was air (40∼400 Torr) and the condensing vapour was water.
On applying an exponentially decaying high voltage pulse, the first cloud track appears on the anode point as a “bead”, and grows to a “boss” and then, the positive streamers shoot out from a circular rim of this “boss”.
When the electric field is adequate a “bead” forms also on the cathode point and, when the electric field at the tip of the negative point becomes appropriately strong by approaching of a positive streamer or of an anode “boss”, a cathode streamer or “spike” dashes out from this “bead” to meet the positive streamer or the anode “boss” at a point one-fourth or one-third of the gap length from the anode. Then a filamentary conducting streamer starts from the anode.
As ion current passes, an air stream is formed near the point electrode causing the shape and position of the pre-onset streamers to be altered. When both air streams collide with each other a track figure of ring shape results.