Temporal separation of the density fluctuation signal measured by light scattering

On Tore Supra, the frequency spectra of the turbulent fluctuations often have 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 time, the density fluctuations convected in the parallel direction from those in the anti-parallel direction with respect to the analysing wavevector. Two signals are thus extracted out of one. The validity of our model is experimentally checked by comparing the auto-correlation coefficients and the frequency spectra computed for the whole and the separated signals. Consequently, the frequency spectrum is studied in detail as a function of the analysing wavenumber leading to an accurate determination of some plasma properties.