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Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2017 > Séminaires 2017 > Le lundi 6 novembre à 11 heures

Le lundi 6 novembre à 11 heures

E.A. Kuznetsov (a,b,c)

(a)P.N. Lebedev Physical Institute RAS, 53 Leninsky Ave., 119991 Moscow, Russia
(b)Space Research Institute RAS, 84/32 Profsoyuznaya str., 117997, Moscow, Russia
(c) Novosibirsk State University, 2 Pirogov str., 630090, Novosibirsk, Russia

Titre/title : Mirror structures in a plasma with pressure anisotropy
Quand/When : Lundi 6 Novembre, 11 heures
Lieu/Where : salle CPHT Aile 0

Résumé : This talk is devoted to a nonlinear theory of mirror structures in a plasma with pressure anisotropy. Such structures are typical for space plasma, can be met in the planet magnetosphere and are often related to the mirror instability. In the first part of this paper we present our results concerning the weakly nonlinear regime of the mirror instability in the framework of an asymptotic model. This model belongs to the class of gradient type systems for which the free energy can only decrease in time. It reveals a behavior typical for subcritical bifurcations : below the mirror instability threshold, all localized stationary structures are unstable, while above threshold, the system displays a blow-up behavior. It is shown that taking the electrons into account (non-zero temperature) does not change the structure of the asymptotic model. For bi-Maxwellian distributions functions for both electrons and ions, the model predicts the formation of magnetic holes. The second part of this paper contains recent results concerning two-dimensional steady mirror structures which can form in the saturated regime. In particular, based on Grad-Shafranov-like equations, a gyrotropic plasma, where the pressures in the static regime are only functions of the amplitude of the local magnetic field, is shown to be amenable to a variational principle with a free energy density given by the parallel tension. This approach is used to demonstrate that small-amplitude static holes constructed slightly below the mirror instability threshold identify with lump solitons of KPII equation and turn out to be unstable. It is also shown that regularizing effects such as finite Larmor radius corrections cannot be ignored in the description of large-amplitude mirror structures. Using the gradient method, which is based on a variational principle for anisotropic MHD taking into account ion finite Larmor radius effects, we demonstrate the results for various mirror structures which appear in 2D numerical simulations : onedimensional magnetic structures in the form of stripes and two-dimensional bubbles when the magnetic field component transverse to the plane is increased. These structures realize minimum of the free energy.

Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)