Forced diffusion effects in the simulation of a non-transferred DC arc

High speed gas flows are experienced through a direct current (DC) electric arc in spacecraft electric propulsion systems, in supersonic plasma torches used for thermal plasma assisted chemical vapor deposition (CVD), in wire arc spraying, in sliding or gliding arcs, and in gas blast circuit breakers. Simulations of such flows typically involve the flow of a compressible gas from low subsonic to supersonic speeds plus the strong heating of the gas by an electric current. To obtain an accurate description of the arc-flow interaction, finite rate chemistry and the selective influence of the electromagnetic field on the charged particles must be included. To predict the anode arc attachment, it is necessary to resolve forced diffusion or drift diffusion velocities in order to drive the charged particles through the strong axial bulk flow. A generalized explicit and implicit forced diffusion scheme is introduced and examined in the context of a two-dimensional computational model of a reacting Ar-H₂ constricted non-transferred DC arc plasma in a convergent divergent supersonic anode nozzle.