Cold-Electrode Characteristics in Shock-Ionized Air Plasmas

The conduction of electric current between cold electrodes in a high-velocity, shock-ionized air plasma has been studied experimentally in order to investigate conduction mechanisms in continuum boundary layers and sheaths. Current-voltage measurements were made in the test flow behind the incident shock wave in an arc-driven shock tube. The electrode configuration employed was of a shielded, parallel-plate type. The data for the lowest, presaturation range of electrode voltages are shown to be in satisfactory agreement with the results of a recent theoretical analysis. Several mechanisms are postulated to explain the observed behavior at the higher values of electrode potential. The current density is shown to be fairly uniform over both electrodes prior to the occurrence of breakdown. The data further indicate that breakdown phenomena occur in the vicinity of the cathode surface.