Collisional-radiative average-atom model for hot plasmas

A collisional-radiative ''average-atom'' (AA) model is presented for the calculation of opacities of hot plasmas that are not in the condition of local thermodynamic equilibrium (LTE). The electron impact and radiative rate constants are calculated using the dipole oscillator strengths of the average atom. A key element of the model is the photon escape probability, which at present is calculated for a semi-infinite slab. The Fermi statistics renders the rate equations for the AA level occupancies nonlinear, which requires iterations until the steady-state AA level occupancies are found. Detailed electronic configurations are built into the model after the self-consistent non-LTE AA state is found. The model shows a continuous transition from the non-LTE to the LTE state depending on the optical thickness of the plasma.