Plasma Effects on Resonant Phenomena

The effect of autoionizing resonances in atomic systems and processes is reviewed. Theoretical framework for treating resonances in the coupled channel approximation using the R-matrix method, as well as approximations related to plasma applications are described. The former entails large-scale atomic computations, and the latter is based on a new method for including collisional, Stark, thermal and other broadening mechanisms. We focus particularly on the problem of opacities calculations in high-energy-density (HED) plasmas such as stellar interiors and inertial confinement fusion devices. The treatment is generally relevant to radiative and collisional processes as the cross sections become energy-temperature-density dependent. While the computational difficulty increases considerably, the reaction rates are significantly affected. The related issue of the Boltzmann-Saha equation-of-state and its variants in local-thermodynamic-equilibrium (LTE) is also explored as the intermediary between atomic data on the one hand and plasma environments on the other.