Berlin 2001 – scientific programme

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P: Plasmaphysik

P 10: Theory and Plasma Diagnostic (Poster Session)

P 10.11: Poster

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

Determination of quenching coefficients by time resolved emission spectroscopy in a hydrogen RF discharge — •T. Gans, V. Schulz-von der Gathen, and H.F. Döbele — Institut für Laser- und Plasmaphysik, Universität Essen, 45117 Essen, Germany

Collisional de-excitation (quenching) can have a pronounced influence on the population of excited states at gas pressures exceeding 10 Pa. The knowledge of quenching coefficients is therefore important for the correct analysis of emission spectra.

CCRF hydrogen plasmas at 13.56 MHz exhibit a field reversal phase of about 10 ns during which an intense electron current provides collisional excitation within the sheath region. Since this short pulsed excitation is strongly dominant, it is possible to determine quenching coefficients from the lifetime of the fluorescence at various pressures (20-400 Pa).

The measured quenching coefficients agree very well with the results reported in connection with laser excitation of the corresponding levels. The inclusion of cascades from higher electronic states is very important. Results for various emission lines, particularly of rare-gases, are presented.

The knowledge of quenching coefficients of rare-gases - admixed in small concentrations - allows us to reveal information on the EEDF. Supported by the DFG in the frame of the SFB 191