Besetzungsdichten angeregter He l-Atome in einem nicht-thermischen Plasma

Abstract

For nonthermal plasmas, the population densities of the ground level and the lower lying excited states can deviate considerably from a SAHA- and BOLTZMANN population density which are only valid for plasmas in (local) thermal equilibrium. To obtain the actual population densities of the lower lying- states of the He I-Atom in a nonthermal, optically thin as well as in a partially optically thick plasma the corresponding rate equations have been solved. Due to the metastable state 23S we have distinguished between the singulet and the triplet system. The coupling between the two systems has been accomplished by appropriate collisional processes. Numerical values are given for the population densities in terms of „SAHA“-population densities for both the lower singlet- and triplet levels in the case of an optically thin plasma. The relaxation times necessary for establishing a steadystate have been calculated. The influence of the triplet-system on the particle densities of the singletsystem is shown. For low electron densities the ratio ni (triplet) /ni (singlet) becomes larger than 3. By solving the complete system of rate equations and comparing the solutions with measured densities one can derive unknown total cross sections for reactions between excited states.