Treatment of ionization in plasma collisional-radiative calculations

In this paper a method for treating electron collisional ionization in collisional-radiative calculations is presented that includes the effects of direct ionization into multiple excited states. Ionization from a given state proceeds to terms of the next ionization state using appropriate cross sections and branching ratios. Level populations are calculated for the case of a low-temperature (7 eV), moderate-density (ne=5×1015 cm−3) ionizing carbon plasma using a time-dependent collisional-radiative model. These results show appreciable differences when compared with calculations in which ionization is assumed to couple only into the ground state of the next ionization stage. Applications of these results to astrophysical and laboratory plasmas are discussed.