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Far Forward Scattering of CO(2) laser radiation from density fluctuations in the poloidal plane (perpendicular to the main magnetic field) of the WVII-A stellarator plasma results in asymmetric distributions of the beat signals in the detector plane of a Fourier lens. It has been attempted to explain the asymmetric profiles with a model which describes scattering from low-M-number quasi-coherent modes. This is equivalent to the picture of the probing beam being scattered from two waves with identical frequency and centre-wavelength propagating at two different positions across the beam in nearly opposite directions; the waves have finite lateral extent transverse to their propagation and the wave fronts are not parallel to one another. Mode numbers detected this way range from about 10 to 30; There exists for a given magnetic field configuration a maximal mode number which is common to all frequencies, i.e. a mode pattern without a finite group velocity. Two existing models, that of laterally extended wave fronts and that of counter-propagating waves, are combined. In addition, lateral wave front profiles other than Gaussian ones are included, and non-parallel fronts are introduced. Finally, EM scattering from fluctuations which are not entirely isotropic is briefly discussed.

Additional information

Authors: MAHN C, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 2/306 EN (1990) 38 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199011024 / Last updated on: 1994-12-01
Original language: en
Available languages: en