Magnetic field reversals in an experimental turbulent dynamoM. Berhanu1, R. Monchaux2, S. Fauve1, N. Mordant1, F. Pétrélis1, A. Chiffaudel2, F. Daviaud2, B. Dubrulle2, L. Marié2, F. Ravelet2, M. Bourgoin3, Ph. Odier3, J.-F. Pinton3 and R. Volk3
1 Laboratoire de Physique Statistique, École Normale Supérieure, CNRS UMR8550 - 24 rue Lhomond, F-75005 Paris, France
2 Service de Physique de l'État Condensé, Direction des Sciences de la Matière, CNRS URA 2464, CEA-Saclay - F-91191 Gif-sur-Yvette, France
3 Laboratoire de Physique, École Normale Supérieure de Lyon, CNRS UMR5672 - 46 allée d'Italie, F-69364 Lyon, France
received 22 December 2006; accepted in final form 12 February 2007; published March 2007
published online 23 February 2007
We report the first experimental observation of reversals of a dynamo field generated in a laboratory experiment based on a turbulent flow of liquid sodium. The magnetic field randomly switches between two symmetric solutions B and -B. We observe a hierarchy of time scales similar to the Earth's magnetic field: the duration of the steady phases is widely distributed, but is always much longer than the time needed to switch polarity. In addition to reversals we report excursions. Both coincide with minima of the mechanical power driving the flow. Small changes in the flow driving parameters also reveal a large variety of dynamo regimes.
91.25.Cw - Origins and models of the magnetic field; dynamo theories.
47.65.-d - Magnetohydrodynamics and electrohydrodynamics.
© Europhysics Letters Association 2007