title: Nonlinear magnetic induction by helical motion in a liquid sodium turbulent flow.
abstract: We report an experimental study of the magnetic field B--> induced by a turbulent swirling flow of liquid sodium submitted to a transverse magnetic field B-->(0). We show that the induced field can behave nonlinearly as a function of the magnetic Reynolds number, R(m). At low R(m), the induced mean field along the axis of the flow, <Bx>, and the one parallel to B-->(0), <B(y)>, first behave like R(2)(m), whereas the third component, <B(z)>, is linear in R(m). The sign of <Bx> is determined by the flow helicity. At higher R(m), B--> strongly depends on the local geometry of the mean flow: <Bx> decreases to zero in the core of the swirling flow but remains finite outside. We compare the experimental results with the computed magnetic induction due to the mean flow alone.
authors.affiliation: Laboratoire de Physique Statistique de l'Ecole Normale Supérieure, CNRS UMR 8550, 24 Rue Lhomond, 75231 Paris Cedex 05, France.
authors.forename: F
authors.initials: F
authors.lastname: Pétrélis
authors.forename: M
authors.initials: M
authors.lastname: Bourgoin
authors.forename: L
authors.initials: L
authors.lastname: Marié
authors.forename: J
authors.initials: J
authors.lastname: Burguete
authors.forename: A
authors.initials: A
authors.lastname: Chiffaudel
authors.forename: F
authors.initials: F
authors.lastname: Daviaud
authors.forename: S
authors.initials: S
authors.lastname: Fauve
authors.forename: P
authors.initials: P
authors.lastname: Odier
authors.forename: J-F
authors.initials: JF
authors.lastname: Pinton