Temporal separation of the density fluctuation signal measured by light scattering

On Tore Supra, the frequency spectra of the turbulent fluctuations often ha ve two peaks centred on some positive and negative values. These two peaks correspond to a poloidal motion of the electrons in opposite directions. In this paper, a criterion is elaborated which allows us to distinguish, in t ime, the density fluctuations convected in the parallel direction from thos e in the antiparallel direction with respect to the analysing wavevector. T wo signals are thus extracted out of one. The validity of our model is expe rimentally checked by comparing the auto-correlation coefficients and the f requency spectra computed for the whole and the separated signals. Conseque ntly, the frequency spectrum is studied in detail as a function of the anal ysing wavenumber leading to an accurate determination of some plasma proper ties.