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P: Plasmaphysik

P 10: Theory and Plasma Diagnostic (Poster Session)

P 10.24: Poster

Wednesday, April 4, 2001, 12:30–15:00, AT2

Absorption measurements in helium and argon plasmas — •Andreas Lotter, Ursel Fantz, and Kurt Behringer — Lehrstuhl für Experimentelle Plasmaphysik, Institut für Physik, Universität Augsburg, 86135 Augsburg

The diagnostics of an ECR–plasma, already equipped with a spectroscopical system, has been extended by the method of absorption spectroscopy. A stabilized xenon arc lamp was used as light source, providing intensive continuum radiation which passes through an optical set up, carried out in Michelson configuration. Pure helium and pure argon plasmas as well as mixtures of helium and argon have been investigated in the pressure range of p=4−20 Pa. In helium, the populations of n=2 levels have been determined. Together with the results of emission spectroscopy, the measured populations of n=2 and n=3 could be compared with results from a collisional–radiative model (ADAS). It will be shown that the metastable levels (2 ¹S) and (2 ³S) have a remarkable influence on the population of higher levels. Furthermore, transitions from the 2 ¹P and 2 ³P states to the ground state and to the metastable states are optically thick, resulting in an enhancement of the populations. For argon plasmas, the populations of both metastable and both resonant levels (3p⁵4s) have been determined, which are typically in the order of 10⁻⁵ of the ground state. In case of argon, the population of each state could be determined by analyzing more than one absorption line, due to the variety of optical allowed transitions. Finally, mixtures of helium and argon have been investigated. The results will be discussed in detail as well as the diagnostic method and the detection limit.