The VKS experiment: turbulent dynamical dynamos

Sébastien Aumaître (1) , Michaël Berhanu (2) , Mickaël Bourgoin (3) , Arnaud Chiffaudel (1) , François Daviaud (1) , Bérengère Dubrulle (1) , Stéphan Fauve (2) , Louis Marié (1) , Romain Monchaux (1) , Nicolas Mordant (2) , Philippe Odier (4) , François Pétrélis (2) , Jean-François Pinton (4) , Nicolas Plihon (4) , Florent Ravelet (1) , Romain Volk (4)

1 SPEC - UMR3680 - Service de physique de l'état condensé
2 LPS - Laboratoire de Physique Statistique de l'ENS
3 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]
4 Phys-ENS - Laboratoire de Physique de l'ENS Lyon

The VKS experiment studies dynamo action in the flow generated inside a cylinder filled with liquid sodium by the rotation of coaxial impellers (the von Karman geometry). We report observations related to the self-generation of a stationary dynamo when the flow forcing is symmetric, i.e. when the impellers rotate in opposite directions at equal angular velocities. The bifurcation is found to be supercritical, with a neutral mode whose geometry is predominantly axisymmetric. We then report the different dynamical dynamo regimes observed when the flow forcing is asymmetric, including magnetic field reversals. We finally show that these dynamics display characteristic features of low dimensional dynamical systems despite the high degree of turbulence in the flow.

Mots clés: Dynamo; Magnetohydrodynamics; Turbulence

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Sébastien Aumaître, Michaël Berhanu, Mickaël Bourgoin, Arnaud Chiffaudel, François Daviaud, et al.. The VKS experiment: turbulent dynamical dynamos. Comptes Rendus. Physique, 2008, 9 (7), pp.689-701. ⟨10.1016/j.crhy.2008.07.002⟩. ⟨hal-00492303⟩