François DAVIAUD

Service de Physique de l'État Condensé, Commissariat à l'Énergie Atomique, Saclay, France

Research interests: non linear and out of equilibrium phenomena, including chaos, granular flows, turbulence, dynamos,...

VKS experiment: a chaotic turbulent dynamo?

The VKS experiment studies dynamo action in the flow generated inside a cylinder filled with liquid sodium by the rotation of coaxial impellers. We first report observations related to the self-generation of a stationary dynamo when the flow forcing is Rπ 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 discuss the role of turbulence in the dynamo mechanism. We then report the different dynamical dynamo regimes observed when the flow forcing is not symmetric: stationary dynamos, transitions to relaxation cycles or to intermittent bursts, and random field reversals. We show that these dynamics result from the interactions of a few modes and display characteristic features of low dimensional dynamical systems despite the high degree of turbulence in the flow. (VKS collaboration: CEA - CNRS - ENS Paris - ENS Lyon).

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R. Monchaux et al. Phys Fluids 21, 025104 (2009)