A comparison between detailed and configuration-averaged collisional-radiative codes applied to non-local thermal equilibrium plasma

Michel Poirier , François de Gaufridy de Dortan (1)

1 SPAM - Service des Photons, Atomes et Molécules

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 Te=10 eV (or higher) but fails at lower temperatures such as Te=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.

Keywords: non-LTE plasmas; plasma kinetic equation; collisional-radiative code; configuration-average; detailed balance; carbon

Domains: Plasma Physics [physics.plasm-ph]

Michel Poirier, François de Gaufridy de Dortan. A comparison between detailed and configuration-averaged collisional-radiative codes applied to non-local thermal equilibrium plasma. Journal of Applied Physics, 2007, 101, pp.063308. ⟨10.1063/1.2713085⟩. ⟨cea-00179289⟩