Microwave transmission measurements in Tore Supra

A microwave transmission diagnostic system below the electron gyrofrequency is now operating on Tore-Supra. In low density Lower-Hybrid current drive discharges the refraction effects are weak and the measurement of the wave transmission coefficient provides an estimate of the non inductive current. For higher densities, the signal is modulated by refraction effects related to sawteeth and MHD modes. In this case, more elaborated computational techniques are required in order to isolate the absorption effect from the apparent wave attenuation due to refraction. Conversely, at frequencies low enough to avoid cyclotron absorption, microwave transmission can be used as a diagnostic of sawteeth and MHD activity