Spark discharges in iodine vapour

Abstract
Sparks in iodine vapour have been studied at pressures between 0.08 and 0.80 Torr, and for gaps of the order of 10 cm. Sparks were initiated in non-uniform fields, using voltage pulses between 1 kV and 3 kV, corresponding to overvoltages of up to 300%. Development of the spark proceeds through a glow phase to a filamentary arc. The glow-arc transition is a two-stage process, involving the formation of a cathode spot, with a corresponding drop in cathode fall voltage, followed by constriction of the positive column, during which molecular dissociation occurs. Following construction, the arc expands radially and a temperature of 5000K and electron density of 6*1012 cm-3 are reached before decay sets in. During spark decay, a transition occurs from an atomic to a molecular arc phase.

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