Berlin 2005 – wissenschaftliches Programm
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P: Plasmaphysik
P 7: Poster: Niedertemperaturplasmen / Plasmatechnologie 3, Diagnostik 3
P 7.13: Poster
Freitag, 4. März 2005, 16:30–18:30, Poster HU
Investigations of short-scale fluctuations in a helicon plasma — •M. Krämer1, A.B. Altukhov2, E.Z. Gusakov2, M.A. Irzak2, V.L. Selenin1, and B. Lorenz1 — 1Experimentalphysik II, Ruhr-Universität Bochum — 2A.F.Ioffe Physico-Technical Institute, St Petersburg
Correlation Enhanced-Scattering (CES) near the Upper Hybrid Resonance has been applied for studying small-scale plasma density fluctuations excited by the rf fields in a high-density helicon discharge. The frequency and wave number spectra of the fluctuations are measured both in the plasma core as well as in the outer region of the helicon discharge. The spectral measurements evidence the short-scale fluctuations to originate from a parametric decay instability. The lf fluctuations and the lower side-band of the helicon wave frequency obey the ion-sound and Trivelpiece-Gould dispersion relations, respectively. To estimate the fluctuation level the back-scattering process is analyzed both numerically and analytically. A fully electromagnetic model was developed that takes into account the radial density profile as well as the antenna diagram of the emitting/receiving horn. Using this model the relative amplitude of ion-sound density fluctuations in the core of the helicon discharge is estimated as 11 %. The findings also demonstrate that the CES diagnostic can be applied to diagnose fluctuations in spherical tokamak plasmas where the probing conditions resemble those of high-density helicon discharges (in particular, ωpe≫ ωce).
Supported by the DFG (SFB 591, Projekt A7)