Detection of lower hybrid waves by coherent scattering of microwaves: Preliminary results in Wega

The coherent scattering of a microwave beam is considered as a diagnostic tool for monitoring the penetration of the lower hybrid heating waves in a plasma. A set up using a 2 mm wavelength has been installed on the Wega torus. Preliminary experimental data are reported and discussed. The amplitude of the electron density fluctuations has been found lower than the one we expected. The variation of the wave amplitude as the plasma density varies, qualitatively agrees with a cold plasma electromagnetic theory. The feasibility of the measurements was checked and indications of some improvements to be made in the diagnostic method came out. Some important topics (both theoretical and practical) in scattering experiments on L.H. heating waves are reviewed.