La réflectométrie: un outil pour détecter les modes MHD dans les plasmas du tokamak Tore Supra

Based on ionosphere radar, reflectometry is a diagnostic that measures the electron density in magnetic fusion devices. The high sensitivity and precision make reflectometry able to detect the density perturbations induced by MHD instabilities. Using plasma rotation, a 2-D image of the density profile can be reconstructed during sawtooth, a core MHD relaxation. Running in fixed frequency mode, reflectometers detect the cut-off layer oscillations induced by MHD modes as fast particles driven MHD modes. A good agreement was obtained between observations and theoretical predictions for acoustic MHD modes (Beta Alfven Eigenmodes) which are excited by fast ions. However, the temporal evolution of the frequency and the structure (frequency splitting) of these modes during a sawtooth is under investigation.