Microwave reflectometry: A sensitive diagnostic for electron density property measurement in Tore-Supra fusion plasmas

Based on radar principle reflectometry measures the electron density in magnetic fusion plasma. On Tore-Supra, six reflectometers measure the density profiles and the properties of density fluctuations with good temporal and spatial resolution. Four swept reflectometers from 33 to 155 GHz provide reliable and accurate measurements of the whole density profile from the edge on the outer side up to the inner side. The sweeping time was recently decreased from 20 to 4 μs. Fast profile evolution can be followed owing to high repetition rate. Density fluctuations are measured with three different techniques. The classical fixed frequency method looks at large scale density fluctuations. Properties of density fluctuations can also be recovered from consecutive frequency sweeps. Doppler reflectometry is based on wave back scattering on small scale density fluctuations. It measures the poloidal rotation and fluctuations amplitude at different wave numbers. Recent numerical simulation of plasma turbulence have recovered the wave number spectrum obtained from Doppler and fast sweep reflectometry. Reflectometry is also sensitive to the density fluctuations induced by magneto hydrodynamic perturbations. Low frequency modes can be localized by fast sweep profile reflectometry. High frequency modes excited by energetic particles accelerated by the plasma heating system are observed with fixed frequency fluctuation reflectometry. (authors)