An Experimental Dynamo in a Highly Turbulent Flow

Philippe Odier, Ecole Normale Superieure, Lyon, France

The dynamo effect is a magnetohydrodynamics instability, allowing the existence of a self-sustaining magnetic field in a flow of an electrically conductive fluid. This effect is considered to be at the origin of the magnetic field of the Earth and the stars. Until now, it had only been evidenced experimentally in cases where internal boundaries guide the flow. I will present the first observation of a dynamo in a homogeneous flow of liquid sodium (VKS2 experiment), where the turbulent fluctuations are of the same order of magnitude as the mean flow. The behavior of this instability close to the threshold will be described, as well as scaling laws for its saturation. One striking feature of such a dynamo, that makes it very different from the previous constrained dynamos, is that it displays a large variety of dynamical regimes, including chaotic reversals, strongly reminiscent of the observed reversals of the Earth's magnetic field.

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