Hot plasma opacities in the presence or absence of local thermodynamic equilibrium

A collisional–radiative model is used to investigate local thermodynamic equilibrium (LTE) versus non-LTE conditions in medium-Z hot plasmas. The model uses the steady-state solution of rate equations within the “average atom” (AA) approximation and subsequently generates the relevant many-electron configurations to proceed to the method of “detailed configuration accounting” (DCA) for the computation of frequency dependent opacities. The key elements of the model are the non-LTE radiative transition rates in the presence of a non-Planckian radiation field and the source function for the radiation transport in the non-LTE plasma. Calculations are presented for aluminum, germanium and bromine plasmas. We present calculations at temperatures where experimental data are available and also at higher temperatures where non-LTE features may be significant.