Using sparse matrices techniques and iterative solvers in the calculation of level populations for NLTE plasmas

Abstract

In this work, we present a steady-state CR model for the calculation of level population in which the sparse matrix technique is employed to store the elements of the CR matrix and we show the utility of iterative methods to solve the rate equations. This procedure allows us to determine the level populations for low-Z plasmas in a detailed level description, which is required for spectroscopic or diagnostics purposes. For intermediate and high-Z plasmas, the use of sparse matrix technique and iterative solvers is not enough to carry out a detailed level calculation, but we show that the combining use of those techniques and simple atomic models, as those based on analytical potentials, makes possible reasonable accurate calculations of average ionizations and ionic populations in a wide range of temperature and electron density conditions. Furthermore, a brief discussion about how the considered energy levels structure affects to average ionization and ionic charge distribution for different plasma conditions is also presented.