Departures from equilibrium in a free-burning argon arc

Abstract

A magnetogasdynamic arc model due to Kovitya and Lowke has been combined with a collisional-radiative model of the argon atom to show how intense radiation from an arc can produce excited-state densities in the boundary of the arc which are far in excess of the densities corresponding to thermodynamic equilibrium. Quantitative predictions based on this model have been compared with measurements recently reported by Farmer and Haddad. There are encouraging similarities between theory and experiment, although it is suggested that the theory could be further improved by including the effect of resonance radiation which is scattered in the arc boundary.