Thèse soutenue

FR
Auteur / Autrice : Luca Marradi
Direction : Thierry PassotFrancesco Califano
Type : Thèse de doctorat
Discipline(s) : Physique des plasmas
Date : Soutenance en 2011
Etablissement(s) : Nice en cotutelle avec Pise, Università degli studi
Ecole(s) doctorale(s) : École doctorale Sciences fondamentales et appliquées (Nice2000-....)
Partenaire(s) de recherche : autre partenaire : Université de Nice-Sophia Antipolis. Faculté des sciences

Résumé

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Two specific aspects of solar wind turbulence at scales comparable with the ion Larmor radius were considered : anisotropic plasma heating, and the electromagnetic spectral properties of the turbulent cascade in the direction perpendicular to the ambient magnetic field. These problems were studied by means of one-dimensional numerical simulations with two different methods : a FLR-Landau fluid (FLR-LF) model that extends anisotropic magnetohydrodynamics by retaining low-frequency kinetic effects such as Landau damping and finite Larmor radius corrections, and a hybrid Vlasov code in 1d-3V phase space dimensions (HV). Preliminary investigations were performed in the context of compressible Hall-MHD that demonstrated a possible Alfvén wave cascade in the parallel direction at scales smaller than the ion inertial length. Simulations of the FLR-LF model in quasi-perpendicular directions with a random forcing aiming at mimicking the tail of the Alfvén cascade show a non-resonant ion perpendicular heating and the development of the mirror instability which constraints the system to remain near instability threshold. The FLR-LF model has been extended to include the effect of a weak amount of collisions described by a BGK operator. Simulations including collisions show a very good agreement with satellite data. We also performed simulations with the HV code where a forcing on the electric fields code was introduced. These simulations showed the generation of a power-law spectrum with slope -5/3 at scales larger than the ion skin depth, and slope -7/3 in the short wavelengths range, together with the formation of “perpendicular shocks” and magnetic holes.