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

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.