Density impact on toroidal rotation in Tore Supra: experimental ă observations and theoretical investigation

International audienceThe 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