AN INVESTIGATION OF ELECTRICAL BREAKDOWN OF A PLASMA-ELECTRODE SYSTEM

Electrical breakdown between a pair of electrodes immersed in a flowing plasma corresponds to the transition between low- and high-current conduction régimes and has been attributed to many causes. In the work reported here, which involved cold electrodes in contact with the plasma produced by an electromagnetic shock tube, it was found that the minimum breakdown voltage corresponded to an average electric field in the cathode sheath of about 2 MV cm-1 over a wide range of plasma conditions. This was probably adequate to initiate the formation of non-thermionic cathode spots, and the voltage-current characteristics in the high-current régime were consistent with a field-emission theory of this mechanism, originally suggested by Smy. Moreover, electric fields in the plasma, sheath thicknesses and mean free paths were such that alternative explanations of the high-current régime were reasonably eliminated.