Analysis of ionization and recombination processes under the coronal equilibrium conditions by using a statistical atomic model

Abstract

Ionization and recombination processes accompanying collisions of free electrons with plasma ions are considered using a statistical atomic model in which ionization and recombination are regarded as the processes of pair electron collisions in the electron gas of an atom. An expression for the ionization rate as a function of the ionization energy I and temperature T is derived. According to this expression, the ionization rate at I ≫ T is proportional to exp(−I/T). The statistical atomic model provides an estimate of the recombination rate for an ion with an arbitrary nuclear charge number Z, whereas more exact calculations of the recombination rate can be performed only for large Z. The model explains relatively low values of I/T (as compared to those given by the Saha equation) under the coronal equilibrium conditions and predicts a reduction in I/T with increasing Z. The values of I/T and the average ion charge number obtained from the balance equation for multielectron ions with the use of one fitting coefficient agree with the tabulated data calculated in the multilevel coronal model.