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
received 25 February 2008; accepted in final form 26 March 2008
published online 7 April 2008
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.
91.25.Cw Origins and models of the magnetic field; dynamo theories
47.65.-d Magnetohydrodynamics and electrohydrodynamics