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P: Plasmaphysik
P 9: Dense Plasmas and Plasma Diagnostic (Poster Session)
P 9.24: Poster
Tuesday, April 3, 2001, 12:30–15:00, AT2
Correlation Enhanced-Scattering on a helicon discharge — •Michael Krämer1, Nina M. Kaganskaya 2, and Valeriy L. Selenin2 — 1Experimentalphysik II, Ruhr-Universität Bochum, D-44780 Bochum — 2Ioffe Physico-Technical Institute, 26, Polytekhnicheskaya st., St. Petersburg, Russia
Enhanced scattering (ES) of microwaves is a new diagnostic which uses the extraordinary (X) wave for probing small-scale fluctuations in magnetized plasmas. When the incident X wave approaches the upper hybrid resonance layer, the wave number grows rapidly up to values much larger than the vacuum wave number. Simultaneously, the amplitude of the incident wave increases and, in the presence of density fluctuations in the resonance region, strongly enhanced back-scattered signals arise if the Bragg condition is fulfilled. The Correlation ES diagnostic is here applied for the first time to diagnose low-frequency fluctuations in a helicon source (pulsed discharge HE-L; fRF=13.56 MHz, ne≤ 2· 1019 m−3, B0<0.1 T, p=0.1−2 Pa argon gas, rp=7.3 cm, Lp=110 cm) for conditions where the electron plasma frequency is much higher than the cyclotron frequency. Fairly coherent ion-sound fluctuations with wavelengths of the order of 1 mm have been detected in the outer region of the helicon plasma. Our investigations offer also prospects for applying the ES technique on compact (spherical) tokamaks.
This work was supported by the Deutsche Forschungsgemeinschaft through the Sonderforschungsbereich 191 (Projekt A12)