Density Fluctuations Measurements on Tore Supra Tokamak Plasma: Radial Profiles and Spectra

Abstract

Up to now, turbulent processes in fusion plasmas are not clearly identified, then innovative and comprehensible diagnostic measurements are required. Fast-sweep heterodyne reflectometry is always suitable for precise measurement of density profiles but can also be used to reconstruct fluctuation density profiles. A closed-loop upgrade of the method developed in [1] , based on comparisons between simulated and experimental reflected signals, allows us to extract from shot to shot on Tore Supra tokamak the density fluctuations radial wavenumber spectra S(k r ) from the fluctuating phase signal of the X-mode fast-sweep V and W band reflectometers.In this paper we focus on the application of this experimental method of extracting the spatial evolution of the wavenumber spectra and radial density fluctuation profiles of the Tore Supra tokamak plasma. Then we exhibit a density fluctuations scaling with the electronic density gradient length L ne .

Density profile and turbulence evolution during L-H transition studied with the ultra-fast swept reflectometer on ASDEX Upgrade

“…A closed-loop minimising method [27] is applied to reduce the difference between the numerical and measured phase spectra. If they are close enough, the input at this iteration is assumed to correspond to the real density fluctuation spectra and to be the unique solution, otherwise the current transfer function is applied to the experimental phase spectra and the result is used as input for the next iteration.…”