Cylindrical probe measurements have been made in an iodine vapour plasma containing a ratio of negative ions to electrons sufficiently large for electron effects to be neglected; that is, in a positive-ion/negative-ion plasma. The ion-ion plasma was produced by allowing plasma from the Faraday dark space of a DC iodine glow discharge to diffuse into a side-arm. Almost symmetrical current-voltage probe characteristics were obtained in the ion-ion plasma, and both the positive and negative current regions were found to follow a (current)2-voltage relationship, as would be expected if ion collection by the probe was orbital-limited. The characteristics were analysed using orbital-limited current theory to provide data on plasma potential, ion number density and Debye length. The results of the analysis are consistent with the dominant ion species in the ion-ion plasma being I2+ and I3−.

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.

Articles you may be interested inModeling of the gain and temperature in high pressure, ejector type chemical oxygen-iodine lasers and comparison to experiments J. Appl. Phys.The chemical composition of iodine vapor has been calculated assuming local thermodynamic equilibrium and using the partition functions of the constituent particle species. Data are presented for three pressures: 0.36 torr, 46 torr, and 1 atm, over the temperature range 400 to 12000 K.

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