Kinetics of Ionization-Recombination of a Plasma and Population Density of Excited Ions. II. Ionizing Plasma

Abstract

A calculation of the quasi-steady-state solution for a purely-ionizing hydrogen plasma shows that each excited level goes through three phases with an increase in electron density, n_e: i.e., the corona phase for low n_e, the quasi-saturation phase for intermediate n_e and the complete-saturation phase for high n_e. In the latter two phases the ladder-like excitation mechanism gives the population density distribution n(p)⁄g(p)∝p⁻⁶ (n(p)⁄g(p) is the population density per unit statistical weight of the level with the principal quantum number p). For this class of plasma Griem’s LTE criterion gives the boundaries between these phases instead of LTE. In the ionization mechanism the ladder-like excitation-ionization process becomes important when the low-lying excited levels enter into the saturation phase, and its contribution amounts to 50% of the total ionization rate for high n_e. An experiment supports these conclusions.