MEASUREMENTS OF THE SUPRATHERMAL ELECTRON-DENSITY PROFILE BY ELECTRON-CYCLOTRON EMISSION AT THE UPPER CUTOFF LAYER IN TORE-SUPRA

The possibility of measuring the radial profile of fast-electron distr ibutions from ECE spectra is discussed. The most usual ECE diagnostic set-up, i.e. the second-harmonic X-mode, observed by low-held side ant ennae in the equatorial plane, can be used by exploiting the reflectio n of spontaneously emitted radiation by the upper cut-off layer and th e length of the sightline between the reflecting surface and the recei ving antenna. The emitted intensity depends on this length, which intr oduces an element of spatial resolution in the suprathermal ECE spectr a. Two methods are proposed. First, a dynamic method is described in w hich the length of the sightline is varied by density perturbations. S econd, a spectral method is discussed that uses the length variation o f the sightline with the observation frequency. A proof of the princip le behind both methods is given for a lower hybrid current driven disc harge in Tore Supra in which a pellet was injected.