A broadband reflectometer operating in the frequency range 50-75 GHz has beendeveloped on Tore Supra to measure electron density profiles at the edge. Thesystem uses extraordinary mode polarization and performs routine measurementsin 20 µs with heterodyne detection to ensure a high dynamic rangesensitivity. It allows separate phase and amplitude information of the signal.The density profiles are fully automatically calculated from the raw phase.The initialization is done with automatic detection of the first cut-offfrom the amplitude of the reflected signal with an accuracy of up to ±0.5 cm. Theprofiles are now part of the public database of Tore Supra and canprovide details of density structures better than the centimetre range. The highreliability of the measurements for various plasma conditions make thisdiagnostic an ideal tool to study specific edge plasma physics with givenexamples on detached plasma behaviour and antenna-plasma coupling processes forion cyclotron resonant frequency and lower hybrid heating powers.It also is shown how the presence of suprathermal electrons may perturb themeasurements.
Application of a stratified plasma model to microwave reflectometry of density fluctuations