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Journée de Dynamique Non Linéaire
Mardi 3 juin,
Attention: lieu inhabituel!! Cette rencontre aura lieu au Centre de Physique Théorique (CPT) de Marseille-Luminy en amphi 5 (5ème étage): 10h00: Alain Brizard St-Michael College, Colchester, Vermont, USA Nonlinear Finite Larmor Radius effects in reduced fluid models The polarization and magnetization effects associated with the dynamical reduction leading to the nonlinear gyrokinetic Vlasov-Maxwell equations are shown to introduce nonlinear finite-Larmor-radius effects into a set of nonlinear reduced-fluid equations previously derived by Lagrangian variational method [A.J. Brizard, Phys. Plasmas 12, 092302 (2005)]. These intrinsically nonlinear FLR effects, which are associated with the transformation from guiding-center phase-space dynamics to gyrocenter phase-space dynamics, are different from the standard FLR corrections associated with the transformation from particle to guiding-center phase-space dynamics. We also present the linear dispersion relation and results from a nonlinear simulation code using these reduced-fluid equations. The simulation results (in both straight and dipole geometries) demonstrate that the equations describe the coupled dynamics of Alfven and sound waves and that the total simulation energy is conserved. 11h00: Pause Café 11h30: Natalia Tronko CPT - Marseille Barrières pour la réduction du transport dû à la dérive E x B On s'intéresse à l'amélioration du confinement d'un plasma de tokamak. On considère la dynamique chaotique de particules chargées due à la dérive E x B des centres guides. Le champ B est considéré constant et uniforme, et le champ électrique est modélisé par le potentiel électrique: V = epsilon \sum_{n,m=1}^N (n^2+m^2)^(-3/2) Cos(n A + m \theta + \phi(n,m) - t) où epsilon = 1/B est un petit paramètre, A est la coordonnée radiale et \theta l'angle poloïdal. Nous construisons un (petit) terme de contrôle additif au potentiel électrique, qui bloque la diffusion radiale des particules, en créant une barrière interne de transport (ITB). On s'intéresse aussi à la robustesse de ce contrôle. Travail en collaboration avec M. Vittot. 11h50: Rodolphe Chabreyrie Mechanical Engineering Department, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA Chaotic Mixing Control within a Translating and Rotating Droplet The elaboration of strategy generating efficient mixing is crucial for a variety of applications including digital microfluidic devices that use microscopic "discrete" fluid volumes (droplets) as microreactors. In this work, we present a strategy that enables the generation and control of such an efficient mixing inside a spherical droplet. Mixing that occurs through stretching and folding of material lines. This strategy is applied to a Stokes flow corresponding to a steady translating droplet by superposing an unsteady rigid body rotation. This strategy that relies on the resonance effects between the steady and unsteady part of the flow offers the possibility of controlling both the size and the location of the mixing within the droplet. Travail en collaboration avec D. Vainchtein, C. Chandre, P. Singh & N. Aubry. |