On various validity criteria for the configuration average in collisional-radiative codes

TL;DR

This paper evaluates the validity of configuration averaging in collisional-radiative models for plasmas by proposing criteria based on partial-rate systems and analyzing their applicability through charge-distribution studies in carbon and neon plasmas.

Contribution

It introduces a detailed criterion for assessing the validity of configuration averaging in collisional-radiative codes, considering different transition types and energy dispersions.

Findings

The criterion is fulfilled when the energy dispersion of configurations is less than the electron thermal energy.

Different forms of the validity criterion are discussed and compared.

Application to carbon and neon plasmas demonstrates the criterion's effectiveness.

Abstract

The characterization of out-of-local-thermal-equilibrium plasmas requires the use of collisional-radiative kinetic equations. This leads to the solution of large linear systems, for which statistical treatments such as configuration average may bring considerable simplification. In order to check the validity of this procedure, a criterion based on the comparison between a partial-rate systems and the Saha-Boltzmann solution is discussed in detail here. Several forms of this criterion are discussed. The interest of these variants is that they involve each type of relevant transition (collisional or radiative), which allows one to check separately the influence of each of these processes on the configuration-average validity. The method is illustrated by a charge-distribution analysis in carbon and neon plasmas. Finally, it is demonstrated that when the energy dispersion of every populated configuration is smaller than the electron thermal energy, the proposed criterion is fulfilled in each of its forms.