Degree of Ionization of a Plasma in Equilibrium

Abstract

Previous investigations derived the SAHA equation for a plasma in equilibrium applying the free-bound concept valid for an isolated electron-ion pair. In our investigation of the “adapted free-bound model” (I) we have shown that due to the free-bound interaction the demarcation between free and bound states is shifted by Δχ=—e2/r0 . We study the influence of this shift of the ionization limit on the effective ionization energy in SAHA’S equation. At the same time we account by interpolation for the contributions of the quasi-free highly correlated particles. The lowering of the free-bound limit causes an increase of the effective lowering of the ionization energy in SARA’S equation beyond the well-known e2/D-term resulting from the free-free interaction. This additional term itself is of the order O (e2/D) and therewith much stronger than the correction found from higher order correlations of the free particles. On the other hand it is much smaller than the lowering of the free-bound limit.