Anode phenomena in a collision-dominated plasma

Anodes display either a glow mode or a constricted mode in plasmas of interest for MHO generator applications. The purpose of this paper is to outline the conditions underlying the existence of anode constrictions or anode spots in conjunction with criteria governing the anode glow. A steady current flowing through velocity and thermal boundary layers is investigated. The sheath and the ambipolar region are considered from an approximation theory viewpoint, and then the nonexistence of a one-dimensional Cartesian or diffuse mode for a nonreacting anode region is shown using the continuum equations for electrostatic probes.This work is supported by the Air Force Office of Scientific Research

Analysis of the voltage drop arising from a collision-dominated sheath

The article of record as published may be found at http://dx.doi.org/10.1063/1.322603Voltage drops associated with the collisional sheath of nonemitting, MHD electrodes are investigated. The problem is described by a set of coupled nonlinear partial differential equations which are solved by finite differencing in a computer. The sheath and ambipolar regions form in a self-consistent way obviating the need to match boundaries. A two-dimensional model with periodic active sites on a flat plate is used. The current constricts at these sites in order to satisfy the controlling equations for frozen charge flow. The effects of a magnetic field as well as of Joule heating are included in the model; convection can be shown to be negligible in the sheath. Joule heating is assumed to have no effect on the bulk temperature of the gas. Changes in the current-voltage characteristics due to Joule heating are small since the effect is extremely localized; the presence of a magnetic field has a slight influence on the size of the sheath but alters noticeably the current-voltage characteristics. (AIP