The role of excited state ionization data on H and He generalized collisional–radiative coefficients

Abstract

We present results of collisional–radiative modelling of H, He and He+ for use in plasma transport studies. Generalized collisional–radiative (GCR) coefficients are generated for each ion using the most recent atomic data available. The data generated cover electron densities up to 1 × 1015 cm−3 and electron temperatures up to about 200 eV. These data are archived online for use by modelling codes. We then present a study on the role of excited state ionization data on GCR coefficients. For most ions, excited state ionization cross sections are not well known. We use the high quality data that are available for H, He and He+ to test two commonly used methods for excited state ionization data, namely, semi-classical methods or perturbative methods. It is found that for neutral H and He, the exchange classical impact parameter (ECIP) method provides accurate data for derived GCR coefficients, while the perturbative distorted-wave methods lead to significant overestimates of the effective ionization rate coefficient. For He+, using perturbative distorted-wave data for the excited state ionization processes gives reasonably accurate results for the GCR coefficients, while the ECIP results significantly underestimate the effective ionization rate coefficient. Thus, for neutral H and He the semi-classical method is to be preferred over the distorted-wave method, and the situation is reversed for He+.