Time-dependent hydrogenic ionization model for non-LTE mixtures

We present an efficient, non-local thermodynamic equilibrium (non-LTE), tim e-dependent ionization model for laser-produced plasmas containing mixtures of elements (species). An ionization distribution for each species which i s consistent with the ambient electron density is obtained by use of an ite rative procedure. Energy levels for each shell having a given principal qua ntum number and for each ion stage of each species in the mixture are calcu lated using screening constants. Steady-state non-LTE as well as LTE soluti ons are also provided. The model is particularly useful at low temperatures where convergence problems are usually encountered. Our results compare we ll with previously published data for selenium. We apply our model to typic al situation in X-ray laser research and laser-produced plasmas. We illustr ate the application to mixtures by calculation an approximate ionization fo r fused quartz at solid density and compare the results with previous calcu lations. (C) 1999 Elsevier Science Ltd. All rights reserved.