Collisional-Radiative Model for Helium-Like Ions : Application to Intermediate-Density Plasmas

In order to interpret the spectral-line intensities emitted from various plasmas, a collisional-radiative-model program has been constructed for heliumlike ions. In this model a population of 61 excited levels is considered, and excitation, deexcitation, ionization and three-body recombination by electron collisions, spontaneous transition, radiative recombination, and dielectronic recombination have been included. For these processes, the most reliable rate coefficients, experimental or theoretical, have been employed. A detailed account is given of the program along with the review of the rate coefficients adopted. As an example of its applications, line-intensity data for theta-pinch plasmas are analyzed; for oxygen the three sets of experiments are consistent with the present calculation. For the case of carbon, however, the intensity ratio cannot be interpreted consistently on the assumption of the ionizing-plasma model. Rather, it is strongly suggested that the plasma has a significant contribution from the recombining-plasma component.