Numerical modeling of the constriction of the dc positive column in rare gases

The constriction of the positive column of a de glow discharge in argon at high pressures is analyzed using the continuity equations for the charged p articles and the gas thermal balance equation coupled with the local electr on Boltzmann equation and a detailed collisional-radiative model for the at omic and ionic species. Contrary to the other existing models of the constr iction in inert gas, the present model is self-consistent and fully detaile d, and provides a quantitative description of all the discharge properties. The numerical techniques used to solve the boundary value problem correspo nding to our set of equations an discussed in detail. The transition from t he diffuse to the constricted state and the properties of this latter state are investigated. The model predicts the existence of multimodal solutions for the discharge parameters as a function of the discharge specific power , within a limited range of values of the latter above a critical value, wh ich explains the observed abrupt changes in the discharge parameters and th e hysteresis associated with constriction. The radial distributions of the gas temperature and of the densities of all neutral and charged species con sidered are determined along with various other discharge characteristics, such as the steady-state discharge maintenance electric field, as a functio n of the discharge operating parameters. The results for argon show satisfa ctory agreement with data from experiments. A few model simulations are fur ther presented that enable one to gain physical insight on the relevant kin etic processes of constriction in argon. Such simulations are instrumental to understanding also the mechanisms of constriction in the other inert gas es. [S1063-651X(99)11703-3].