Project of magnetic fluctuation measurement by cross polarization scattering in the Tore Supra Tokamak

Up to now the direct measurement of the magnetic fluctuations in the core of tokamak plasmas has been impossible. According to various turbulence models, the estimated level of B/B lies between 10-6 (residual magnetic fluctuations due to drift wave i.e. O(βn/n) where β is the toroidal beta) and 10-4 (obtained assuming that the heat transport is only due to magnetic turbulence). We describe in this paper a tentative diagnostic to measure these fluctuations. It is based on the cross polarization scattering: Magnetic fluctuations scatter an incident electromagnetic wave with a change in polarization. In section II the basic principle of the diagnostic is explained. In section III the experimental set up is described. It will be tested on the Tore Supra Tokamak at the end of 1990. (author) 2 refs., 2 figs