STEADY-STATE IONIZATION-BALANCE CALCULATIONS FOR A SELENIUM PLASMA

A steady-state model is used to calculate the ionization balance for a selenium plasma at electron temperatures where the Ne-like stage is dominant. In this model, the ion distribution and free-electron density are calculated for a specified particle density and temperature. In addition, each state of a given ion is connected to appropriate states of the same ion by excitation and deexcitation and connected to the appropriate states of adjacent ions by ionization and recombination. Excited states including autoionizing states are treated explicitly. Rate coefficients for all processes are based consistently on atomic-structure calculations. The calculations indicate that hundreds of electron configurations are necessary to obtain suitable results and that electron configurations must be included consistently across ion stages. Autoionizing states are shown to be the major influence in determining the ionization balance. The use of plane-wave Born collision strengths instead of better distorted-wave collision strengths appears to have a negligible effect on the overall ion stage distribution at moderate densities. The results may explain why F-like lasing transitions were not observed in the experiments by Matthews et al. [Phys. Rev. Lett. 54, 110 (1985)].