An Experimental Investigation of the Conduction of Electric Current Between Cold Electrodes in Shock-Ionized Air Plasmas

摘要

Current-voltage characteristics were measured in the ionized test flow behind the incident shock wave in an arc-driven shock tube. The electrode configuration employed in the experiments was of a shielded type and applied voltages of from 1.5 to approximately 100 volts were used to drive the electrode currents. Data were obtained at shock Mach numbers between 17.5 and 18.6 with an initial pressure of 1 mm Hg in the driven section. The degree of ionization of the test flow was approximately .0006. In the intermediate range of electrode potentials, a mechanism, which is based on a simple ionic resistor model, is proposed to provide a possible explanation of the experimental data. For the highest range of electrode potentials employed, the current approached a limiting value. In all ranges of electrode potential employed the cathode boundary layer is found to play a dominant role in controlling the flow of current. Electrical breakdown was observed in some cases when high electrode voltages were employed. When breakdown occurs, the cathode current becomes extremely nonuniform, with the average cathode current density being more than an order of magnitude greater than the local value measured at the center of the cathode surface. The anode current, on the other hand, remains fairly uniform over the electrode surface. (Author)