Equation of State of Reacting Strongly Coupled Plasmas

Abstract

The equation of state of complex reacting mixtures of partially ionized gases is almost always obtained from a free energy model. Typically this is a pseudo ideal gas free energy minimization calculation in which a particular aspect of the interaction of an atom (or ion) with its surroundings is invoked to cut off the divergence of the atomic partition function [Mchesney, 1964]. This results in some uncertainty in the equation of state even in the zero coupling limit. The Debye Hückel electrostatic free energy is often added to the ideal gas free energy to account for ionic coupling. In more sophisticated calculations additional additive free energy terms to account for the finite size of the atoms (and ions) and other effects are also included [Graboske, Harwood and DeWitt, 1971]. These model approaches grew out of a need to obtain the equation of state of astrophysical mixtures at a time when a consistent fundamental theory was not available. Considerable progress on the theory has been made in recent years. But even now most of the work is concerned with hydrogen plasmas. The recent monograph of Ebeling, Kraeft and Kremp [1977] gives an excellent review of this literature. In the present paper we give a brief review of the theory for plasmas having Z > 1. A more detailed description of most of the material can be found in Rogers and DeWitt [1973] and Rogers [1974].