Investigation of the magnetic field oscillations and reversals

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The research proposal focuses on a numerical study of turbulent dynamo and magnetic field induction, so as to answer scientific issues raised by the Von Karman Sodiuna experiment (VKS). Following the observations of dynamo action in constraint flows of electrically conducting fluids (experiments in Riga, Karlsruhe, 2000), the extension to less constrained and turbulent flows was a natural next step, and it is actively studied by several groups worldwide. The Instrument built by the VKS team in CEA Cadarache produced new and original data about dynamo with magnetohydrodynamics turbulence.The first dynamo observation in an unconstrained, turbulent regime in 2006 in this setup was a worldwide noticed success expecting to shed new light on aspects relevant for astrophysics and geophysics. These hopes were confirmed by the recently first experimental observation of reversals of a dynamo field in a turbulent flow regime.Results are expected concerning open questions regarding the dynamo: what is the effect of turbulent fluctuations on the threshold value? How does the Saturation of the magnetic field depend on the kinetic Reynolds number? What are the statistical properties of the magnetic and velocity fields both before and after onset? And especially in this new particular project: How are the reversals and oscillations of the magnetic fields triggered?In the numerical studies, the influence of fluctuations and turbulence onto the dynamo threshold will be first explored. The response to an imposed magnetic field will then be studied, as a function of the distance to the dynamo threshold, in order to understand experimental results. Then the Saturation of the dynamo instability as a function of the Reynolds number will be explored. Finally, the reversals and oscillations of the magnetic fields will be investigated.