Étude du transport turbulent dans les plasmas du tokamak Tore Supra : observation des écoulements perpendiculaires stationnaires et du mode acoustique géodésique

Abstract : Tokamaks are toroidal machines designed to magnetically confine plasma and to host reactions of nuclear fusion. Their performance is limited by turbulent transport, which precise mechanisms are not fully elucidated. Turbulent fluctuations cause the onset of macroscopic mean flows, in the direction perpendicular to both magnetic field and small radius, called zonal flows. Their shear is known to decrease both fluctuation level and transport. Diagnostics of Doppler backscattering have been installed on Tore Supra (CEA Cadarache). They could measure the perpendicular velocity of turbulent fluctuations in different zones of the plasma. First, it is shown that, on average, fluctuations flow twice as fast at the low field side of the machine than at its top. The difference, significantly higher than predicted by common models, is put in perspective with the properties of magnetic equilibrium and the behaviour of fluctuations. Then, variations of the velocity, due to the zonal flow branch called geodesic acoustic mode (GAM), are examined in a series of experiments where collisionality is varied. Those observations have been quantitatively compared with a gyrokinetic simulation with the code GYSELA, using the equilibrium profiles from the experiments. GAM frequency in experiments is lower than predicted, especially at low collisionalities. In addition, the instationarity of GAM has been characterized with the Hilbert-Huang transform. Burts of GAM oscillations have similar statistics between experiments and simulation and their duration could be related with the nonlinear interaction between the GAM and turbulence and with the continuum damping which is observed in the simulation.
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Contributor : Alexandre Storelli <>
Submitted on : Thursday, June 25, 2015 - 1:54:02 AM
Last modification on : Friday, May 10, 2019 - 1:54:14 PM
Long-term archiving on : Friday, October 9, 2015 - 5:23:24 PM

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  • HAL Id : tel-01167913, version 1

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Alexandre Storelli. Étude du transport turbulent dans les plasmas du tokamak Tore Supra : observation des écoulements perpendiculaires stationnaires et du mode acoustique géodésique. Physique des plasmas [physics.plasm-ph]. École Polytechnique, 2015. Français. ⟨tel-01167913v1⟩

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