Doppler backscattering system for measuring fluctuations and their perpendicular velocity on Tore Supra

Backscattering of a microwave beam launched in oblique incidence makes possible measurement of density fluctuations close to the cut-off with a selected wave number (k) over right arrow (perpendicular to)=-2 (k) over right arrow (i), where k(i) is the beam wave vector at the reflection layer. On the system installed on Tore Supra, the incidence of the Gaussian beam is controlled thanks to a tiltable monostatic antenna. The microwave part of the system is based on a fluctuation reflectometer scheme with heterodyne detection, and the choice of a V band (50-75 GHz) microwave source and O mode polarization is appropriate for typical enhanced plasma regimes (n(0)=3-7x10(19) m(-3)). Both the scattering wave number k(perpendicular to) and the scattering localization r/a can be changed during a shot, owing to the steppable probing frequency and the motorized antenna (tilt angle 0-10degrees). The wave-number range k(perpendicular to) is 4-15 cm(-1), with a wave-number resolution around 2 cm(-1), and the localization r/asimilar to0.3-0.85. The Doppler effect also provides the perpendicular velocity profile for the same position range. Experiments confirm the diagnostic capabilities. (C) 2004 American Institute of Physics.