Direct observation of the turbulent emf and transport of magnetic field in a liquid sodium experiment

Kian Rhabarnia (1) , Benjamin P. Brown (1) , Mike M. Clark (1) , Elliot J. Kaplan (1) , Mark D. Nornberg (1) , Alex M. Rasmus (1) , Cary B. Forest (2) , Frank Jenko (3) , Angelo Limone (3) , Jean-Francois Pinton (4) , Nicolas Plihon (4) , Gautier Verhille (5)

1 Center for magnetic self organization in Laboratory and Astrophysical Plasmas
2 Center for magnetic self organization in Laboratory
3 IPP - Max-Planck-Institut für Plasmaphysik [Garching]
4 Phys-ENS - Laboratoire de Physique de l'ENS Lyon
5 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre

For the first time, we have directly measured the transport of a vector magnetic field by isotropic turbulence in a high Reynolds number liquid metal flow. In analogy with direct measurements of the turbulent Reynolds stress (turbulent viscosity) that governs momentum transport, we have measured the turbulent electromotive force (emf) by simultaneously measuring three components of velocity and magnetic fields, and computed the correlations that lead to mean-field current generation. Furthermore, we show that this turbulent emf tends to oppose and cancel out the local current, acting to increase the effective resistivity of the medium, i.e., it acts as an enhanced magnetic diffusivity. This has important implications for turbulent transport in astrophysical objects, particularly in dynamos and accretion disks.

Domaines: Dynamique des Fluides [physics.flu-dyn]; Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux

Kian Rhabarnia, Benjamin P. Brown, Mike M. Clark, Elliot J. Kaplan, Mark D. Nornberg, et al.. Direct observation of the turbulent emf and transport of magnetic field in a liquid sodium experiment. The Astrophysical Journal, 2012, 759 (2), pp.80. ⟨10.1088/0004-637X/759/2/80⟩. ⟨hal-00783147⟩