gyrofluid models

Coherent magnetic structures such as magnetic vortex chains have been observed in the solar wind close to the Earth by the Cluster space mission (Perrone et al. (2016, 2017)). Making use of a gyrofluid model, we investigate the existence of analytical solutions of magnetic vortex type and study their stability. The adopted model can provide a nonlinear description of turbulent collisionless magnetized plasmas accounting for ion finite Larmor radius, equilibrium temperature anisotropy and fluctuations of the component of the magnetic field parallel to the direction of a strong and uniform guide field. The model possesses a noncanonical Hamiltonian structure which provides a convenient framework for the use of analytical tools, such as the Energy-Casimir method for determining stability conditions. We carry out investigations for some asymptotic regimes of the model, such as for instance in the limit of a large ion-to-electron perpendicular equilibrium temperature ratio, with negligible electron inertia effects, and compare our results with those found recently in the framework of a reduced magnetohydrodynamics model (Jovanovic et al. 2018).

• D. Perrone, O. Alexandrova, O. W. Roberts, S. Lion, C. Lacombe, A. Walsh, M. Maksimovic and I. Zouganelis. The Astrophysical Journal, 849:49, 2017

• D. Perrone, O. Alexandrova, A. Mangeney, M. Maksimovic, C. Lacombe, V. Rakoto, J. C. Kasper, and D. Jovanović. The Astrophysical Journal, 826:196, 2016

• D. Jovanović, O. Alexandrova, M. Maksimović, M. Belić. J. Plasma Phys., vol. 84, 2018

Reduced fluid models provide a useful tool for qualitative investigations of low-frequency phenomena in plasmas, in the presence of a strong, mean component of the magnetic field. Applications of such models include, for example, magnetic reconnection and turbulence, both in laboratory and astrophysical plasmas. In particular, when investigating phenomena occurring on scales comparable with the ion Larmor radius, the so called reduced gyrofluid models become especially relevant. In the non-dissipative limit, reduced gyrofluid models are supposed to possess a Hamiltonian structure, as is the case for all dynamical plasma models. In addition to its relevance for guaranteeing correct qualitative properties of the dynamics, the knowledge of the Hamiltonian structure can also be of use, for instance, for the identification of families of invariants, particularly relevant in the two-dimensional limit, or for stability analyses. In this talk I will present a rather general framework for deriving a class of Hamiltonian reduced gyrofluid models accounting for equilibrium temperature anisotropies and magnetic perturbations parallel to the mean magnetic field, which could make such models relevant for applications to space plasmas.