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P: Fachverband Plasmaphysik

P 9: Poster: Niedertemperaturplasmen

P 9.17: Poster

Tuesday, March 31, 2009, 17:30–19:30, Foyer des IfP

Argon ion velocity distributions in a helicon discharge measured by laser induced fluorescence — •Dirk Luggenhölscher¹, Yi-Kang Pu², Yusuf Celik¹, and Uwe Czarnetzki¹ — ¹Institute for Plasma and Atomic Physics, Ruhr University Bochum, Germany — ²Department of Engineering Physics, Tsinghua University, Beijing, China

Helicon discharges allow the generation of high density plasmas although operated at low pressure around 0.1 Pa. Here the ion velocity distribution in an argon discharge is studied experimentally. The Helicon discharge is generated by a flat coil antenna operated at 13.56 MHz in an azimuthally isotropic m = 0 mode. The Helicon wave develops as a standing wave confined along the static magnetic field lines between the antenna and the chamber bottom (distance 50 cm). Ion velocity distributions along and perpendicular to the static magnetic field are measured by laser induced fluorescence spectroscopy on metastable argon ions. The measurements reveal that two groups of ions exist, one cold group with a temperature close to the spectral resolution limit and a hot group with a temperature close to the electron temperature, i.e. several eV. The velocity distribution measurements are supplemented by probe measurements of the ion density, the electron energy distribution, and the floating and plasma potentials. Possible heating mechanisms for the ions are discussed. Candidates are wave heating, temperature and density gradients, and a double-layer in the divergent magnetic field.