Reduced models accounting for parallel magnetic perturbations: gyrofluid and finite Larmor radius–Landau fluid approaches

• Published in: Journal of plasma physics Vol. 82; no. 6; p. 049902; 092116; 082502; 102306; 325810103; 034007
• Main Authors: Tassi, E., Sulem, P. L., Passot, T.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.12.2016
• Subjects: Asymptotic properties; Computational fluid dynamics; Electron pressure; Energy conservation; Fluctuations; Fluid mechanics; Fluids; Formalism; Ion velocity; Larmor radius; Magnetic fields; Magnetohydrodynamics; Mathematical analysis; MHD; Nonlinear dynamics; Plasma physics; Temperature; The Vlasov Equation: From Space to Laboratory Plasma Physics; plasma nonlinear phenomena; space plasma physics
• ISSN: 0022-3778; 1469-7807
• DOI: 10.1017/S0022377816000921

Reduced models are derived for a strongly magnetized collisionless plasma at scales which are large relative to the electron thermal gyroradius and in two asymptotic regimes. One corresponds to cold ions and the other to far sub-ion scales. By including the electron pressure dynamics, these models improve the Hall reduced magnetohydrodynamics (MHD) and the kinetic Alfvén wave model of Boldyrev et al. (2013 Astrophys. J., vol. 777, 2013, p. 41), respectively. We show that the two models can be obtained either within the gyrofluid formalism of Brizard (Phys. Fluids, vol. 4, 1992, pp. 1213–1228) or as suitable weakly nonlinear limits of the finite Larmor radius (FLR)–Landau fluid model of Sulem and Passot (J. Plasma Phys., vol 81, 2015, 325810103) which extends anisotropic Hall MHD by retaining low-frequency kinetic effects. It is noticeable that, at the far sub-ion scales, the simplifications originating from the gyroaveraging operators in the gyrofluid formalism and leading to subdominant ion velocity and temperature fluctuations, correspond, at the level of the FLR–Landau fluid, to cancellation between hydrodynamic contributions and ion finite Larmor radius corrections. Energy conservation properties of the models are discussed and an explicit example of a closure relation leading to a model with a Hamiltonian structure is provided.