A collective infraGred laser scattering diagnostic has been installed on the TORE SUPRA tokamak for the measurement of plasma density fluctuations. For the range of wavenumbers explored (3-15cm-'), the scattering angles are very weak (-1 mrad). Consequently, the scattering signals are averaged along the whole observation chord, resulting in poor longitudinal spatial localization. However, by virtue of the pitch angle variation of the magnetic field lines in the tokamak, and of the perpendicularity of the turbulence wavevector 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 justiiy this novel concept.From the variation of the fluctuation power with the orientation angle of the observed wavevector, 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 k-3 dependence for k>6cm-'. Experimental evidences are put foward to show that the k-spectrum is neither purely poloidal nor purely radial in the (k,k,) plane.

The level of density fluctuations is shown to decrease during ergodic divertor operation in Tore Supra. This decrease of the turbulence is correlated with the onset of a temperature pedestal and a local improvement of the confinement. This pedestal is located close to the electric shear layer, i.e. within a narrow region between the plasma core and the ergodic layer. The onset of such a pedestal explains why the central electron temperature is not changed when the ergodic divertor is switched on, in spite of an ergodic zone where the temperature is low

Results on confinement and turbulence from a set of Ohmic discharges in TORE SUPRA are discussed. Attention is focused on the saturation of the energy confinement time and it is emphasized that this saturation can be explained by a saturation of the electron heat diffusivity. The ion behaviour is indeed governed by dilution and equipartition effects. Although the ion heat transport is never neoclassical, there is no enhanced degradation at saturation. This behaviour is confirmed by turbulence measurements using CO2 laser coherent scattering. The level of density fluctuations follows the electron heat diffusivity variations with the average density. Waves propagating in the ion diamagnetic direction are always present in turbulence frequency spectra. Thus, the saturation cannot be explained by the onset of an ion turbulence. The existence of ion turbulence in the edge at all densities cannot be excluded. However, this ion feature in scattering spectra could be explained by a Doppler shift associated with an inversion point of the radial electric field at the edge

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2014 Nous présentons des résultats expérimentaux sur la transition vers la turbulence d'écoulement convectif de l'air en cavité parallélépipédique horizontale de facteur d'aspect 14. On observe des régimes dépendant du temps du type monopériodique et quasipériodique. La fréquence de l'oscillateur monopériodique dépend linéairement du nombre de Rayleigh pour la gamme étudiée : 14 000 Ra 30 000. Abstract. 2014 Experimental results are presented for the transition to turbulence of the air convective flow in horizontal parallelepipedic box of aspect ratio 14. We observe periodic and quasiperiodic time dependence. The monoperiodic oscillator frequency depends linearly of the Rayleigh number within the range 14 000, 30 000.

No abstract

Several discharges have been analysed in Tore Supra in order to improve the understanding of anomalous transport. In ohmic discharges, it has been shown that both particle and heat diffusion coefficients improve with increasing density, then saturate. The level of edge density fluctuations behave in the same way. In the presence of additional heating, the bulk and the edge turbulences behave differently. The level of edge density fluctuations remains constant in most discharges with additional heating (up to 8 MW). In practice, it only depends on edge conditions. On the contrary, the level of core magnetic fluctuations increases systematically with any additional power. Finally, a lowering of the level of the edge density fluctuations has been observed when using the Tore Supra ergodic divertor. This improvement is accompanied by the onset of a temperature pedestal between the plasma bulk and the ergodic layer. This explains why the global confinement remains unchanged in presence of the ergodic divertor in spite of the reduced radius of the last closed magnetic surface.