Étude de la microturbulence par réflectométrie dans un plasma de fusion sur le tokamak Tore-Supra

Abstract : Fast-sweeping reflectometry in extraordinary mode allows direct measurement of radial wavenumber local spectra S(_n/n](kr, r), and radial profiles of density fluctuations, on Tore Supra tokamak. Wavelet-based approach - a mathematical tool for position-frequency analysis - made possible to consider the strong radial variation of the measured turbulence. Special consideration was given to the validation of spectra and turbulent profiles measurements, by comparing with experimental measurements (reflectometries, probes) and numerical non-linear gyrokinetic simulations. This density fluctuations measurement method has been used to analyse the local transport, by performing a dimensionless scaling on collisionnality, __. The scaling experiments allow direct comparisons of plasmas from different tokamaks. A clear decrease of the normalized confinement time of the plasma energy with the normalized collisionnality was observed : B_E _ __-0.5±0.15. These new measurements of density fluctuations profiles have shown an intense rise of the edge turbulence (r/a > 0.8) when increasing - also observed by Doppler reflectometry diagnostic - providing a physical explanation of the loss of confinement with the normalized collisionnality. More central regions did not present apparent variations (_n/n, _eff). Core plasma simulations (linear stability code KineZero and non-linear gyrokinetic GYRO) were performed, in order to analyse the experimental behaviour of the plasma.
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Thomas Gerbaud. Étude de la microturbulence par réflectométrie dans un plasma de fusion sur le tokamak Tore-Supra. Autre [cond-mat.other]. Université Henri Poincaré - Nancy 1, 2008. Français. ⟨NNT : 2008NAN10086⟩. ⟨tel-01748427⟩

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