LOCALIZED MEASUREMENTS OF TURBULENCE IN THE TORE SUPRA TOKAMAK

A collective infra-red laser scattering diagnostic has been installed on the TORE SUPRA tokamak for the measurement of plasma density fluctu ations. For the range of wavenumbers explored (3-15 cm-1), the scatter ing angles arc very weak (approximately 1 mrad). Consequently, the sca ttering signals are averaged along the whole observation chord, result ing in poor longitudinal spatial localization. However, by virtue of t he pitch angle variation of the magnetic field lines in the tokamak, a nd of the perpendicularity of the turbulence wavevector to these field lines, it has been possible to obtain partial spatial resolution alon g the direction of the beam. Good agreement between the experimental a nd theoretical angular resolution of the diagnostic as well as the res ults of cross-correlation performed on the signals obtained by two sim ultaneous probing beams also justify this novel concept. From the vari ation of the fluctuation power with the orientation angle of the obser ved wavevector, it has been possible to deduce the radial fluctuation profile by a deconvolution procedure, showing that the fluctuations in crease sharply near the edge. The k-spectrum was also measured and sho ws a k-3 dependence for k > 6 cm-1. Experimental evidences are put for ward to show that the k-spectrum is neither purely poloidal nor purely radial in the (k(r) - k(theta)) plane.