Hannover 2020 – scientific programme
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P: Fachverband Plasmaphysik
P 8: Low-temperature plasma and applications
P 8.4: Talk
Tuesday, March 10, 2020, 14:55–15:10, b302
Experimental benchmark of radiation transport calculations in low pressure low temperature hydrogen discharges — •Stefan Briefi1, 2, Frederik Merk1, Roland Friedl2, Caecilia Fröhler2, and Ursel Fantz1, 2 — 1Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany — 2AG Experimentelle Plasmaphysik, Universität Augsburg, 86135 Augsburg, Germany
In a discharge, the emissivity of the atomic hydrogen Lyman series is strongly affected by reabsorption of photons resulting in an underestimation of the population densities determined from VUV spectroscopy. This effect can be corrected via line escape factors. In general, the required correction increases with the atomic hydrogen density nH. For 1018 < nH < 1020 m−3 typical for low pressure plasmas, the correction can reach orders of magnitude making a careful benchmark inevitable.
Measurements have been carried out at a planar ICP at varying pressure (1 to 10 Pa) and RF power (700 to 1000 W) with an intensity-calibrated VUV spectrometer for determining the emissivity of the Lyman series up to Lζ (n = 7). In addition, the population of the n=2 state of atomic hydrogen was measured with tunable diode laser absorption spectroscopy on the Balmer-α line. Furthermore, the population of the higher lying states up to n = 7 is obtained from optical emission spectroscopy. The latter two diagnostics are not affected by reabsorption and hence the obtained population densities are used as reference values. They are matched very well when correcting the populations derived from VUV spectroscopy with line escape factors.