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P: Fachverband Plasmaphysik

P IV: Poster: Niedertemperaturplasmen II, Astrophysikalische Plasmen, Magnetischer Einschluss, Plasma-Wand-Wechselwirkung

P IV.10: Poster

Thursday, March 13, 2008, 16:00–18:30, Poster C2

Detection of the negative ion density in oxygen helicon discharges — •Nadiya Sydorenko¹, Olaf Grulke^{1, 2}, and Thomas Klinger^{1, 2} — ¹Max-Planck-Institute for Plasma Physics, EURATOM Association, Greifswald — ²Ernst-Moritz-Arndt University, Greifswald

The investigation of negative ion plasmas has gained a lot of attention, e.g. in the context of the generation of high energy particle beams and plasma processing in semiconductor fabrication. Although studies of negative ion densities have been done intensively in low-density discharges, very limited experimental results are available in discharges with high density. The experimental device VINETA is well suitable for the production of high density (n 10¹⁹ m⁻³ ) magnetised plasmas (B=100mT) with negative ions. Comparative measurements of the spatiotemporal behavior of negative ions in a pulsed RF discharge in oxygen with argon admixtures will be presented. Negative ions are studied experimentally by laser induced photodetachment using a frequency doubled Nd:YAG laser. In addition, negative ion densities are measured with Langmuir probes. The probe data is evaluated by applying two methods: the first one is based on the comparison of saturation currents measured in different gas mixtures [1], while the second is based on the theoretical interpretation of measured current voltage characteristics using a test function. It will be demonstrated that the negative ion concentration depends on the gas pressure, argon admixture, RF power and scales with the plasma density. [1]M. Shindo, Plasma Sour. Sci.Technol. 12 (2003).