Greifswald 2009 – scientific programme

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P: Fachverband Plasmaphysik

P 8: Niedertemperaturplasmen

P 8.13: Talk

Tuesday, March 31, 2009, 16:50–17:05, INP-Staffelgeschoß

Standing Waves and Landau Damping in a Flat Coil Helicon Discharge — •Yusuf Celik, Dragos L. Crintea, Christopher Isenberg, Rachel Fainblat, Drik Luggenhölscher, and Uwe Czarnetzki — Institute for Plasma and Atomic Physics, Ruhr University Bochum, 44780 Bochum

The field structure and the heating mechanism in a Helicon discharge in Argon are investigated. The discharge is excited by a flat coil antenna in the azimuthally isotropic m = 0 mode. Radial B-Dot measurements confirm that the azimuthal B field component is proportional to the derivative of the axial component. An analysis of transversal wave vector spectra demonstrates that mainly one transversal wave vector contributes to the axial helicon field. Operation is only possible at certain ratios of power to static magnetic field strength. These ratios are identified as modes of standing waves by axial B-Dot probe measurements. In modes showing a strong damping of the wave, the inferred phase velocity is close to the electron thermal velocity. The electron density and temperature are obtained by Langmuir probe measurements. An analytical standing wave model including Landau damping and Coulomb collisions reproduces very well the experimental results. From this comparison it can be clearly concluded that Landau damping of electrons travelling along the field lines at speeds close to the helicon phase velocity is the main damping mechanism. Supported by DFG via GK 1051.