A comparison between detailed and configuration-averaged collisional-radiative codes applied to nonlocal thermal equilibrium plasmas

• Published in: Journal of applied physics 2007-03, Vol.101 (6), p.063308-063308-9
• Main Authors: Poirier, M., de Gaufridy de Dortan, F.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; APPROXIMATIONS; AUTOIONIZATION; CARBON; COMPARATIVE EVALUATIONS; ELECTRON TEMPERATURE; ELECTRONS; EQUILIBRIUM PLASMA; EV RANGE 01-10; ION TEMPERATURE; REACTION KINETICS; THERMAL EQUILIBRIUM; THERMODYNAMICS
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2713085

A collisional-radiative model describing nonlocal-thermodynamic-equilibrium plasmas is developed. It is based on the HULLAC (Hebrew University Lawrence Livermore Atomic Code) suite for the transitions rates, in the zero-temperature radiation field hypothesis. Two variants of the model are presented: the first one is configuration averaged, while the second one is a detailed level version. Comparisons are made between them in the case of a carbon plasma; they show that the configuration-averaged code gives correct results for an electronic temperature T e = 10 eV (or higher) but fails at lower temperatures such as T e = 1 eV . The validity of the configuration-averaged approximation is discussed: the intuitive criterion requiring that the average configuration-energy dispersion must be less than the electron thermal energy turns out to be a necessary but far from sufficient condition. Another condition based on the resolution of a modified rate-equation system is proposed. Its efficiency is emphasized in the case of low-temperature plasmas. Finally, it is shown that near-threshold autoionization cascade processes may induce a severe failure of the configuration-average formalism.