A simplified numerical model for atomic processes of the low and medium Z-ions in the laser-produced plasmas

To calculate the ion fractional abundance of every charge state with the short computation time, we tried to build a suitable model for describing atomic processes. In 1982, Busquet proposed a mixed model, where he introduced two superlevels. They are related to a ground state and a ionized state, respectively, and the local-thermodynamic equilibrium (LET) is assumed over the excited states with the ionized state. In order to treat the atomic processes more accurately, we introduce the three superlevels which are the ground state, the first excited state and ionized state. The transition rates between them are evaluated by using Burguess formula which is used in the rate equations. The present model (Extended Mixed Model; EMM) gives results closer to the collisional-radiative model (CRM) than the original mixed model. The emissivity calculated by average-ion model (AIM) is compared with the one by EMM. The x-ray spectra are also obtained by using the EMM together with the hydrodynamic implosion code HIMICO. (author)