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A collective infra-red laser scattering diagnostic has been installed on the Tore Supra tokamak for the measurement of plasma density fluctuations. For the range of wave numbers explored (3-15/cm), the scattering angles are very weak (approximately 1 mrad). Consequently, the scattering signals are averaged along the whole observation chord, resulting in poor longitudinal spatial localisation. However, by virtue of the pitch angle variation of the magnetic field lines in the tokamak, and of the perpendicularity of the turbulence wave vector to these field lines, it has been possible to obtain partial spatial resolution along the direction of the beam. Good agreement between the experimental and theoretical angular resolution of the diagnostic, as well as the results of cross-correlation performed on the signals obtained by two simultaneous probing beams, also justify this novel concept. From the variation of the fluctuation power with the orientation angle of the observed wave vector, it has been possible to deduce the radial fluctuation profile by a deconvolution procedure, showing that the fluctuations increase sharply near the edge. The k-spectrum was also measured and shows a /k3 dependence for k greater than 6/cm. Here, experimental evidence is put forward to show that the k-spectrum is neither purely poloidal nor purely radial in the (k(r)-k(theta)) plane.

Additional information

Authors: DEVYNCK P ET AL, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);GERVAIS F ET AL., PMI-Ecole Polytechnique, Palaiseau (FR)
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion
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