Mixed model: Non-local-thermodynamic equilibrium, non-coronal-equilibrium simple ionization model for laser-created plasmas

An ionization model, partly time dependent, is presented. It is convenient for modeling laser-created plasmas and simple enough to be used in short computer simulations. This model, called the mixed model (MM), is built by gathering excited bound levels and free levels of a same-charge state into one superlevel and by assuming partial local-thermodynamic equilibrium over those levels. Transition rates between two superlevels can then be computed. Its structure allows the development of the MM for inner-shell excitation and ionization, ionization-potential lowering, and Fermi statistics of bound electrons. Mean electron number, spectroscopic ratios, and radiative losses are calculated in the steady-state case. Comparison with other ionization models are made and MM calculations give better agreement with experiments. Furthermore, simple approximation formulas are given for specific energy and mean electron number of high-atomic-number materials.