Bremen 2017 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 28: Helmholtz Graduate School III

P 28.4: Vortrag

Donnerstag, 16. März 2017, 15:15–15:40, HS 1010

Argon LIF Measurements in a high-power helicon discharge — •Nils Fahrenkamp, Birger Buttenschön, and Olaf Grulke — Max Planck Institute for Plasma Physics, 17491 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 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 Prf≤ 100 MW/m−3. The peak plasma density shows a transient behavior over the discharge 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 radial neutral gas and ion density profile with high temporal resolution. Detailed measurements of the neutral pumping effect for various operation parameters and neutral gas inlet options are presented with special emphasis on its effect on the peak metastable density and the plasma density dynamics. The results are compared with a zero dimensional reaction rate model developed for low temperature argon plasmas and plasma density measurements of a CO2-interferometer setup. Calculations of temporally resolved radial electron temperature profiles are shown using atomic line intensity ratio measurements.

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