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P: Plasmaphysik
P 23: Poster: Plasmatechnologie, Plasma-Wand-Wechselwirkung, Staubige Plasmen, Plasmadiagnostik
P 23.12: Poster
Wednesday, March 20, 2002, 17:40–18:40, HZO Foyer
He-I Recombination into the Metastable 23S State in the Vicinity of a Material Surface — •R. Reusch1, B. Koch2, H. Beyer3, P. Kornejew2, and W. Bohmeyer2 — 1Humboldt-Universität zu Berlin, 10115 Berlin — 2Max-Planck-Institut für Plasmaphysik, Bereich Plasmadiagnostik, EURATOM Ass., 10117 Berlin — 3Technische Fachhochschule Wildau, 15745 Wildau
In fusion experiments the heat flux to the walls of the vessel and the target plates is an important issue. While in the case of high electron temperatures the energy flux onto a surface is mainly governed by the kinetic energy of electrons and ions, at low electron temperatures the energy contributed by recombination at the material surface (typically ≈ 10-30 eV/ion) becomes essential. At the PSI-2 facility extensive studies have been performed concerning the energy flux onto a biased target at low electron temperatures (1-10 eV) and moderate plasma densities (≈ 1017 m−3) [1]. While for D and Ar such a recombination related contribution to the energy flux density could be substantiated, in case of He it was found to be significantly lower. This missing part may be attributed to recombination into the metastable 23S state. Recently the neutral gas density and the fraction of metastables in the vicinity of the target have been determined. The densities of neutral He in ground state and in the 23S state were measured by passive spectroscopy and laser induced fluorescence measurements, respectively. While the fraction of He in the 23S state is found to increase when approaching the target surface, as expected, the absolute values, however, are lower than estimated.
[1] Koch, B., et al., J. Nucl. Mater. 290:653-657, 2001.