Rational surface localization and MHD activity measurements using fast sweep reflectometry on Tore Supra

Investigations on magnetohydrodynamics (MHD) modes using X-mode frequency modulated continuous wave reflectometry have been realized on Tore Supra. Two heterodyne reflectometers operating between 50-75 GHz and 75-110 GHz probe the low field side of the plasma, and the detection of the magnetic islands is performed through the perturbations recorded onto the phase and amplitude of the reflected signal. Fast sweep technique associated with a high repetition rate provides a high radial resolution with a high temporal resolution (up to 20 kHz). The radial localization of rational surfaces is achieved along with the measured density profile. Detection of the time of flight discontinuities in combination with equilibrium code calculations of the current profile allows for the accurate determination of core plasma MHD modes at the q ≤ 1 and q ≤ 2 rational surfaces. Continuous sweeping gives detailed analysis of the radial and poloidal structure of the magnetic island.