Equilibrium Properties and Equation of State of a Hydrogen Plasma

Equations are developed for the equilibrium composition and thermodynamic properties of a three-component hydrogen plasma. These are based on a formulation of the total Helmholtz free energy for the system, including corrections to ideal gas behavior due to electrostatic interactions and plasma perturbation of the bound electronic states of hydrogen atom. When a shielded Coulomb potential is used for the perturbation of the bound states and a Debye approximation for the collective electrostatic interactions, it turns out that for low-density, low-temperature plasmas, i.e., ≤${10}^{20}$ electrons/cc and a few electron volts, the bound-state correction, which has been largely ignored, is much more important than the electrostatic correction. The results of a specific calculation based on this model are analyzed and compared with indirect hydrogen plasma temperature-density measurements and with other theoretical calculations based on different approximate free-energy formulations.