Bochum 2002 – wissenschaftliches Programm
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P: Plasmaphysik
P 21: Poster: Grundprobleme, Theorie, Plasmatechnologie, Astrophysikalische Plasmen
P 21.15: Poster
Montag, 18. März 2002, 17:40–18:40, HZO Foyer
Parametric instability in a helicon discharge observed by Cross-Correlation Enhanced Scattering — •Valeriy L. Selenin1, Nina M. Kaganskaya1, and Michael Krämer2 — 1Ioffe Physico-Technical Institute, St. Petersburg, Russia — 2Experimentalphysik II, Ruhr-Universität Bochum, D-44780
Enhanced scattering (ES) of microwaves close to the Upper Hybrid Resonance layer is a relatively new method for detecting small-scale fluctuations or waves in non-uniform magnetized plasmas. By applying the cross-correlation scheme of this diagnostic, we measured the frequency and wave number spectra of the fluctuations excited et the edge of the helicon discharge HE-L (ne ≤ 2· 1019m−3,PHF ≈ 2 kW, f=13.56 MHz, Te≈ 4 eV, B<0.2 T, p≈ 1 Pa argon, rp=7.4 cm, Lp=110 cm). Part of the spectrum can be attributed to ion-sound turbulence. The ES signal reveals a threshold at a certain RF power thus proving the nonlinear nature of the fluctuations. Their dispersion perpendicular to the magnetic field suggest that the turbulence originates from a parametric decay of the helicon modes. We also present recent measurements of the frequency and the wave number spectra of the fluctuations as well as its growth rate and RF power dependence carried out in the centre of the helicon discharge.
(Supported by the DFG, SFB 191, Project A12 & Russian-German Contract 146 RUS 590, and the Grant supporting Scientific Schools 96-15-96367.)