Effect of magnetic boundary conditions on the dynamo threshold of von Kármán swirling flows

Christophe Gissinger1,2, Alexey Iskakov3,4, Stephan Fauve 1 and Emmanuel Dormy2,3

1 Laboratoire de Physique Statistique, 4 Ecole Normale Sup4erieure CNRS - 24 rue Lhomond, F-75005 Paris, France, EU
2 Laboratoire de Radioastronomie, 4 Ecole Normale Supérieure CNRS - 24 rue Lhomond, F-75005 Paris, France, EU
3 Institut de Physique du Globe de Paris - Paris, France, EU
4 U.C.L.A., Physics Department - Los Angeles, CA, USA

EPL (Europhysics Letters), 82 29001 (2008).

received 25 February 2008; accepted in final form 26 March 2008
published online 7 April 2008


91.25.Cw Origins and models of the magnetic field; dynamo theories
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Abstract. We study the effect of different boundary conditions on the kinematic dynamo threshold of von Kármán type swirling flows in a cylindrical geometry. Using an analytical test flow, we model different boundary conditions: insulating walls all over the flow, effect of sodium at rest on the cylinder side boundary, effect of sodium behind the impellers, effect of impellers or side wall made of a high-magnetic-permeability material. We find that using high-magneticpermeability boundary conditions decreases the dynamo threshold, the minimum being achieved when they are implemented all over the flow.