Determination and analysis of the thermodynamic regimes of xenon plasmas

Abstract

Xenon is a common element employed, for example, as impurity in magnetically confined plasmas or the medium in which radiative shocks propagate in laboratory astrophysics. In both situations, it is required the knowledge of plasma parameters such as the average ionization, the charge state distribution, the atomic level populations and the radiative properties. In most cases, the plasmas are under non‐local thermodynamic equilibrium (NLTE) conditions and these quantities should be determined by means of the so‐called collisionalradiative models. For a high Z element like xenon this is a complex task and entails a high computational cost since it is necessary to solve a very large set of rate equations. In this work are characterized the thermodynamic regimes of xenon plasmas as a function of the matter density and temperature. This fact will allow us to establish in which regions of density and temperature the assumption of local thermodynamic equilibrium (LTE) is accurate and also in which regions it can be retained to estimate some plasma parameters but not others. Moreover, it is also provided information about the average ionization in a wide range of plasma conditions which covers both LTE and NLTE regimes which is valuable information in order to optimize subsequent calculations. Finally, it is also performed an analysis of the differences of NLTE and LTE simulations on several relevant plasma parameters. With this purpose, a comparison is made between the results of the calculation using detailed NLTE modeling with simulations that use the same energy level structure, but atomic populations that are forced into LTE (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)