Analyse spectrale des mécanismes de propagation et de dissipation de la turbulence dans les plasmas de vent solaire et de tokamaks

Abstract : This thesis takes part in the study of spectral transfers in the turbulence of magnetized plas- mas. We will be interested in turbulence in solar wind and tokamaks. Spacecraft measures, first principle simulations and simple dynamical systems will be used to understand the mechanisms behind spectral anisotropy and spectral transfers in these plasmas. The first part of this manuscript will introduce the common context of solar wind and tokamaks, what is specific to each of them and present some notions needed to understand the work presented here. The second part deals with turbulence in the solar wind. We will present first an obser- vational study on the spectral variability of solar wind turbulence. Starting from the study of Grappin et al. (1990, 1991) on Helios mission data, we bring a new analysis taking into account a correct evaluation of large scale spectral break, provided by the higher frequency data of the Wind mission. This considerably modifies the result on the spectral index distribution of the magnetic and kinetic energy. A second observational study is presented on solar wind turbulence anisotropy using autocorrelation functions. Following the work of Matthaeus et al. (1990); Dasso et al. (2005), we bring a new insight on this statistical, in particular the question of normali- sation choices used to build the autocorrelation function, and its consequence on the measured anisotropy. This allows us to bring a new element in the debate on the measured anisotropy depending on the choice of the referential either based on local or global mean magnetic field. Finally, we study for the forst time in 3D the effects of the transverse expansion of solar wind on its turbulence. This work is based on a theoretical and numerical scheme developped by Grappin et al. (1993); Grappin and Velli (1996), but never used in 3D. Our main results deal with the evolution of spectral and polarization anisotropy due to the competition between non- linear and linear (Alfvén coupling, solar wind transverse expansion) mechanisms. Comparison with observations prooves the efficiency of this model. The third and last part deals with spectral transfers in tokamaks. The Gysela simulation and the turbulence in this model will be introduced to the reader. We bring a new diagnostic tool aimed at the understanding of the radial transport of turbulence in the sheared magnetic field of a tokamak. We bring new elements to the question of spectral organisation of avalanches. The toroïdal coupling is known to relax the energy from ITG instabilities into ballooning modes. We debate its role in the radial propagation of avalanches. We also bring a new reduced model to try and understand these different turbulent mechanisms with minimal hypothesis.
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Submitted on : Saturday, September 12, 2015 - 4:30:56 AM
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  • HAL Id : tel-01114244, version 2

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Yue Dong. Analyse spectrale des mécanismes de propagation et de dissipation de la turbulence dans les plasmas de vent solaire et de tokamaks. Physique des plasmas [physics.plasm-ph]. Ecole Polytechnique, 2014. Français. ⟨tel-01114244v2⟩

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