title: Optimum reduction of the dynamo threshold by a ferromagnetic layer located in the flow.
abstract: We consider a fluid dynamo model generated by the flow on both sides of a moving layer. The magnetic permeability of the layer is larger than that of the flow. We show that there exists an optimum value of magnetic permeability for which the critical magnetic Reynolds number for dynamo onset is smaller than for a nonmagnetic material and also smaller than for a layer of infinite magnetic permeability. We present a mechanism that provides an explanation for recent experimental results. A similar effect occurs when the electrical conductivity of the layer is large.
authors.affiliation: Laboratoire de Physique Statistique, Ecole Normale Supérieure, CNRS, Université Pierre et Marie Curie and Université Paris Diderot, Paris, France.
authors.forename: J
authors.initials: J
authors.lastname: Herault
authors.affiliation: Laboratoire de Physique Statistique, Ecole Normale Supérieure, CNRS, Université Pierre et Marie Curie and Université Paris Diderot, Paris, France.
authors.forename: F
authors.initials: F
authors.lastname: Pétrélis
mesh_terms: D055590:Electromagnetic Phenomena; D059346:Magnets; D008962:Models, Theoretical; D009038:Motion