Hannover 2016 – scientific programme

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P: Fachverband Plasmaphysik

P 5: Poster Session- Helmholtz Graduate School for Plasma Physics

P 5.20: Poster

Monday, February 29, 2016, 16:30–19:00, Empore Lichthof

Neutral Argon measurements in a high-power helicon discharge — •Nils Fahrenkamp, Birger Buttenschön, and Olaf Grulke — Max Planck Institute for Plasma Physics, 17489 Greifswald, Germany

The laser-induced-fluorescence (LIF) method is a widely used non-invasive technique to gain information about the velocity distribution, temperature and density of the plasma ions and the neutral gas. It has often been speculated that neutral gas pumping represents an important mechanism limiting the plasma density in high-power helicon discharges. Prometheus-A is an extremely high-power helicon discharge using multiple, spatially distributed helicon antennas to achieve rf power densities up to P_rf≤ 100 MW/m⁻³. The peak plasma density over the discharge shows a transient behavior and decreases with a typical time scale of ≈ 1 ms, which indicates the importance of the neutral gas inventory. LIF is used to measure the neutral gas density profile with high spatial resolution. The excitation vacuum-wavelength for the metastable argon atoms of 667.91 nm is provided by a diode laser system and the fluorescence signal of 750.39 nm is collected by an external pick-up optic, filtered and detected by a photomultiplier tube. Detailed measurements of the neutral pumping effect for various operation parameters are presented with special emphasis on its effect on the peak plasma density and compared with a zero dimensional reaction rate model developed for low temperature argon plasmas.