Electronic edition ISSN 1574-0579

Large scale analysis of the von Kármán sodium experiment using proper orthogonal decomposition

V. Botez , R. Bousquet , C. Nore

Laboratoire Interdisciplinaire des Sciences du Numérique, CNRS, Campus universitaire Paris-Saclay, rue du Belvédère, 91400 Orsay, France

Abstract
In 2006, the von Kármán sodium (VKS) experiment was able to produce a dynamo effect using liquid sodium driven by two counter-rotating impellers in a cylindrical cavity. We analyze simulations of this setup both in growth and saturated dynamo regimes using the Proper Orthogonal Decomposition (POD). In the growth phase, the magnetic field generated is essentially an axial dipole supplemented with secondary structures which are shown to be emerging from the usual α-effect. The most surprising result is found in the saturated phase, where the magnetic field feedback breaks the symmetry of the velocity field even though it is in an exactly counter-rotating configuration. Figs 9, Refs 25.