Voltage-current Characteristics of MHD Boundary Layer Plasmas

Abstract

This paper deals with a two-dimensional time-dependent numerical simulation of the growth of discharges in MHD generator boundary layers. The calculated voltage-urrent characteristics in a boundary layer have positive resistance characteristics for small currents and negative ones for large currents. The characteristics agree with those observed in an anodic layer of actual ETL-Mark 7 B-channel experiments for various temperatures of electrodes. The current flows almost uniformly into the electrode surface (diffuse or fine constricted mode) when the current density is in the region of positive V-I characteristics. It concentrates in a large diameter (large constricted mode) in the region of negative ones. The critical current for this transition of discharge mode is about 0.5 A/㎠ for cold electrodes. This value becomes larger for hot electrodes.