München 2019 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 18: Postersitzung

P 18.11: Poster

Donnerstag, 21. März 2019, 16:30–18:30, Foyer Audimax

Measurements of the H (n = 2) Density via Laser Absorption Spectroscopy — •Frederik Merk1, Roland Friedl1, Caecilia Fröhler1, Stefan Briefi1,2, and Ursel Fantz1,21AG Experimentelle Plasmaphysik, Universität Augsburg, 86135 Augsburg, Germany — 2Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany

The n=2 density of atomic hydrogen or deuterium in low pressure low temperature plasmas can be accessed by emission spectroscopy of the Lyman-α line at 122 nm. However, an absolutely intensity calibrated vacuum ultraviolet (VUV) spectrometer is required and opacity effects due to reabsorption of emitted photons affect the measurement. The latter problem can be solved by applying the escape factor method, which on the other hand raises large error bars to the n=2 density. A direct way to measure the H (D) (n=2) density is the use of tunable diode laser absorption spectroscopy on the Balmer-α line at 656 nm, allowing also to analyse the transition’s line profile. The built up system consists of a laser which is tunable in the wavelength range between 652 nm and 660 nm. The change of the frequency of the emitted photons is monitored by an etalon. The system is installed, tested and characterized at a planar ICP discharge (RF 2 MHz, power up to 2 kW). Here, measurements of the n = 2 density of both hydrogen and deuterium are performed for plasmas under varying pressure and applied RF power. The obtained values are compared to escape factor corrected VUV spectroscopy measurements. Additionally, a comparison to the collisional radiative model Yacora H is perfomed.

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