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International audience; The effect of plasma density on toroidal rotation was examined in ă density ramp-up experiments at a plasma current of 1 MA and a toroidal ă magnetic field of 3.6 T in Tore Supra ohmic discharges. Experimental ă measurements have shown that the toroidal rotation amplitude is reduced ă at all radii when increasing the plasma density, although it remains in ă the countercurrent direction. Neoclassical predictions including ă ripple-induced toroidal friction are in qualitative agreement with such ă observations. However, in the core (r/a < 0.5) the plasma accelerates at ă n(l) similar to 3 x 10(19) m(-2) and breaks again above n(l) similar to ă 3.5 x 10(19) m-2. This rotation bifurcation did not appear to be ă correlated to a possible influence of the sawtooth activity. ă Nonetheless, quasi-linear gyrokinetic simulations have shown that the ă transition of the nature of linear microinstabilities from ITG-TEM to ă pure ITG occurs at n(l) similar to 3 x 10(19) m-2, which could indicate ă a change on the turbulence driven contributions and explain the ă deviation from neoclassical predictions in the plasma core.

20th International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI), Forschungszentrum Julich, Aachen, GERMANY, MAY 21-25, 2012; International audience; We report the results of an experimental investigation of the impact of Supersonic Molecular Beam Injection in the Tore Supra tokamak. Several diagnostics were synchronised with the injection to extract a global picture of the physics at play from the time scale of turbulence (similar to 10 mu s) to the full-recovery time (similar to 1 s). As previously reported, a strong impact of the injection on density and temperature profiles is observed. Both fields exhibit a complex dynamic response involving different phases and time scales. In particular, we show that the effective particle fuelling efficiency is determined by a period of degraded confinement that follows the injection, during which the edge density collapses, in some cases, lower than the initial one. This phase is characterised by a dramatic change in the turbulent transport, with a drop of the frequency spectrum and the observation of large coherent structures as opposed to small intermittent fluctuations before the injection.

International audience; The influence of changing collisionality on density fluctuation characteristics is studied during dedicated ν∗ scaling experiments, using Doppler backscattering system. First, the repartition of fluctuation energy over different spatial scales, as represented by the wavenumber spectrum, is investigated and a modification of the shape of the perpendicular wavenumber spectrum in the low wavenumber part of the spectrum is observed when changing collisionality. In addition, a new procedure to evaluate the dispersion relation of micro-turbulence is presented. From the behavior of the perpendicular mean velocity of density fluctuations with the perpendicular wavenumber, different dispersion relations are obtained between low and high collisionality cases.