Collisional Ionization Equilibrium

Abstract

Collisional ionization equilibrium (CIE) (sometimes called coronal equilibrium from its application to the hot coronae of stars) is a dynamic balance at a given temperature between collisional ionization from the ground states of the various atoms and ions present in the plasma and the process of recombination from the higher ionization stages. In this equilibrium, effectively, all ions are in their ground state. Collisional ionization equilibrium is to be distinguished from the ionization balance which is achieved under conditions of local thermodynamic equilibrium (LTE). LTE is described by the Saha equation which is frequently used in stellar theory. The Saha equation describes a different equilibrium from the coronal approximation because in LTE, the excited states are all populated according to Boltzmann’s law. These excited states play an important role in determining the ionization state of the medium.

“Hangs in the uncertain balance of proud time”

— Robert Greene