Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence - CNRS - Centre national de la recherche scientifique Accéder directement au contenu
Article Dans Une Revue Journal of Plasma Physics Année : 2015

Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence

Résumé

The role of magnetic helicity is investigated in kinetic Alfvén wave and oblique whistler turbulence in presence of a relatively intense external magnetic field b 0 e ||. In this situation, turbulence is strongly anisotropic and the fluid equations describing both regimes are the reduced electron magnetohydrodynamics (REMHD) whose derivation, originally made from the gyrokinetic theory, is also obtained here from compressible Hall magnetohydrodynamics (MHD). We use the asymptotic equations derived by Galtier and Bhattacharjee (2003 Phys. Plasmas 10, 3065-3076) to study the REMHD dynamics in the weak turbulence regime. The analysis is focused on the magnetic helicity equation for which we obtain the exact solutions: they correspond to the entanglement relation, n ñ = -6, where n and ñ are the power law indices of the perpendicular (to b 0) wave number magnetic energy and helicity spectra, respectively. Therefore, the spectra derived in the past from the energy equation only, namely n = -2.5 and ñ = -3.5, are not the unique solutions to this problem but rather characterize the direct energy cascade. The solution ñ = -3 is a limit imposed by the locality condition; it is also the constant helicity flux solution obtained heuristically. The results obtained offer a new paradigm to understand solar wind turbulence at sub-ion scales where it is often observed that -3 < n < -2.5.

Dates et versions

hal-01551982 , version 1 (30-06-2017)

Identifiants

Citer

Sébastien Galtier, Romain Meyrand. Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence. Journal of Plasma Physics, 2015, 81 (1), pp.325810106. ⟨10.1017/S0022377814000774⟩. ⟨hal-01551982⟩
147 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More