Modeling of nonstationary vacuum arc plasma jet interaction with a neutral background gas

Abstract

A plasma beam formed by a stationary vacuum arc source with a copper cathode is considered as a supersonic hydrodynamic jet interacting by collisions with a neutral atmosphere of background gas (argon). The plasma jet propagation in the neutral atmosphere is calculated numerically using a one-dimensional approximation. The values assumed at the entrance cross section of the plasma jet were ion temperature 104 K, electron temperature 3×104 K, ion concentration ni=1019 m−3 plasma jet mass velocity 1.5×104 m/s, and neutral concentration of (0.1,1,2,5)×ni. Two cases were analyzed:(1) isothermal gas motion and (2) gas motion with energy transfer from the ions to the neutrals. It is found for the isothermal case that the plasma front expands with decreasing velocity, but it never decreases down to the speed of sound. A snowplow effect is found with respect to the neutral gas. The neutral gas is accelerated by the plasma jet up to supersonic velocity. With ion–neutral energy transfer the plasma jet deceleration leads to shock discontinuities for all studied neutral densities.