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Descriptions fluide et cinétique d'une turbulence d'interchange dans un plasma magnétisé

Abstract : The kinetic and fluid descriptions of the interchange instability are compared in the linear and non-linear regimes. The prediction of the turbulent transport in tokamaks is the general framework. The kinetic model is two dimensional in space, and one dimensional in energy. The fluid analogue retains the dynamics of both density and pressure. The closure, which acts on the heat flux, is collisional. The fluid system is shown to be equivalent to two Vlasov-type equations for two distinct monokinetic distribution functions. This allows one to use the same numerical tool to run non-linear simulations in kinetic and fluid. For similar linear characteristics, the level of heat turbulent transport is larger in fluid than in kinetics, by orders of magnitudes. Zonal flows do not explain the whole discrepancy. As a matter of fact, the distribution function departs significantly from a maxwellian, so that the adopted closure is failing. An alternative collisionless closure is proposed. It aims at fitting the quasi-linear entropy production rates. In this case, the kinetic and fluid linear properties can be made similar.
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https://hal.univ-lorraine.fr/tel-01748082
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Emmanuel Fleurence. Descriptions fluide et cinétique d'une turbulence d'interchange dans un plasma magnétisé. Autre [cond-mat.other]. Université Henri Poincaré - Nancy 1, 2005. Français. ⟨NNT : 2005NAN10141⟩. ⟨tel-01748082⟩

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