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Abstract

Ordinary wave reflectometry in a plasma containing a localized density perturbation is studied with a 1-dimensional model. The phase response is studied as a function of the wavenumber and position of the perturbation. It is shown that it strongly depends upon the perturbation shape and size. For a small perturbation wavenumber, the response is due to the oscillation of the cut-off layer. For larger wavenumbers, two regimes are found : for a broad perturbation, the phase response is an image of the perturbation itself; for a narrow perturbation, it is rather an image of the Fourier transform. These features are enhanced for a broadband perturbation (modulated square wave) and scattering can occur over the whole region up the cut-off. The phase response obtained for a damped square perturbation is in excellent agreement with the results of an earlier experiment (Rhodes et al, Phys. Fluids 1992) whereas the Gaussian pulse cannot reproduce them. For tokamak plasmas it turns out that, for the fluctuation spectra usually observed, the phase response comes primarily from those fluctuations that are localized at the cut-off. Finally, the results of a 2-dimensional model show that geometry effects are negligible for the scattering by radial fluctuations.

Additional information

Authors: FANACK C, Université Henri Poincaré, Laboratorie de Physique des Milieux Ionisés, Vandoeuvre (FR);BOUCHER I, Université Henri Poincaré, Laboratorie de Physique des Milieux Ionisés, Vandoeuvre (FR);HEURAUX S, Université Henri Poincaré, Laboratorie de Physique des Milieux Ionisés, Vandoeuvre (FR);LECLERT G, Université Henri Poincaré, Laboratorie de Physique des Milieux Ionisés, Vandoeuvre (FR);CLAIRET F, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);ZOU X L, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Report: 1570 EN (1996) 17pp.
Availability: Available from Association Euratom-CEA, CEN Cadarache, 13108 Saint-Paul-lez-Durance (FR)
Record Number: 199610652 / Last updated on: 1996-06-10
Category: PUBLICATION
Original language: en
Available languages: en
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