Vacuum arc plasma jet interaction with neutral ambient gas

Vacuum are plasma jet (VAPJ) propagation in a neutral nitrogen atmosphere has been calculated numerically on the basis of a hydrodynamic description. It was assumed that the VAPJ was emitted isotropically from a point source located z(0) = 20 mm in front of the entrance of a straight duct 100 mm in diameter in which an axial magnetic field of 0.02-0.05 T was imposed. Plasma densities of n(0) = 10(18) and 10(19) m(-3) and neutral gas densities n(n0) = 0.001-0.1 x n(0) were used as initial conditions at the duct entrance. A three-fluid model was used, with the ion temperature having an initial value at the duct entrance of T-i = 10(4) K, while constant temperatures of T-e = 3 x 10(4) K and T-n = 10(3) K were assumed for the electrons and neutrals, respectively. It was found that the plasma jet decelerates down to the critical point, i.e. where the jet velocity is equal to the local speed of sound. The distance of the critical point from the entrance cross section decreased from z(c) = 4 x R (R = radius of duct) for n(n0) = 0.001 x n(0) down to z(c) = R for n(n0) = 0.1 x n(0). It was found that increasing the magnetic field also decreased z(c). It was also found that the electrons and ions have rotational motion components, in opposite directions, and that friction with the neutral gas decreases the rotational velocities.