INTERNAL MAGNETIC FLUCTUATIONS AND ELECTRON HEAT-TRANSPORT IN THE TORE-SUPRA TOKAMAK - OBSERVATION BY CROSS-POLARIZATION SCATTERING

Magnetic fluctuations (radial size approximate to 5 mm) are measured b y a cross polarization scattering (CPS) diagnostic in Tore Supra. In t he scenario O + (B) over tilde --> X, only the poloidal component of t he magnetic fluctuations is measured, while both the radial and the po loidal component are measured in the scenario X + (B) over tilde --> O . These fluctuations are investigated quantitatively in the ohmic and low confinement regimes over a wide range of plasma currents, densitie s and additional heating powers. At the same time, the electron heat d iffusivities expected from these fluctuations are compared with those obtained by profile analysis. Three main results are obtained: (a) The radial profile of the poloidal magnetic fluctuations in the gradient region (0.3 < r/a < 0.7) is established from these measurements. The m agnetic fluctuation levels are found to increase towards the plasma ed ge, and this feature is compatible with that of electron heat diffusiv ity. (b) A strong correlation between the measured magnetic turbulence and the local temperature gradient is observed during the additional heating. (c) The local electron heat diffusivity induced by magnetic f luctuations is estimated using the non-collisional quasi-linear formul a chi(e)(mag) = pi qRv(th)(delta B-r/B)(2)(,) where the radial compone nt of the magnetic turbulence is assumed to be of the same order as th e poloidal component. Both the order of magnitude and the parametric d ependence of chi(e)(mag) show similarities with electron diffusivities determined by transport analysis. In particular, a threshold is obser ved for the dependence of fluctuation induced heat fluxes on the local temperature gradient, which is close to the critical gradient observe d for the measured heat fluxes.