Partial equilibrium and relaxation in a plasma

Abstract

This paper describes a study of the behavior of nitrogen and argon plasmas at about 4000°K temperature and 10 Pa pressure. Experiments show that such plasmas exhibit several possibilities of physical and chemical nonequilibrium. In the case of nitrogen, chemical relaxation phenomena which may be initiated by small-amplitude disturbances are first considered, in order to identify accurately the chemical kinetics of the plasma. Several reactive models were investigated; concentrations at chemical equilibrium and characteristic process times were computed in several cases. The influence of radiative processes, and that of various types of thermal freezing were investigated, leading to determination of the most probable reactive process. It is shown that full equilibrium is highly unlikely, whereas partial equilibrium is possible. Partial chemical equilibrium computations at one temperature were performed. Coupled relaxation processes at several temperatures were then investigated, and the laws governing the phenomena established. Two phenomena were investigated more specifically: • —relaxation behind a shock, • —relaxation after nitrogen injection into an argon plasma.