Laboratory experiments on dynamo action and magnetorotational instability
Intervenant : Frank Stefani
Helmholtz Zentrum, Dresde (Allemagne)
Magnetic fields of planets, stars and galaxies are produced by the homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once generated, magnetic fields can foster cosmic structure formation by destabilizing, via the magnetorotational instability (MRI), Keplerian flows that would be otherwise hydrodynamically stable.
For a long time, both effects had been the subject of purely theoretical and numerical research. This changed in 1999 when the threshold of magnetic-field self-excitation was crossed in the two liquid sodium experiments in Riga and Karlsruhe . Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest, such as field reversals and excursions. Liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, and Socorro have contributed further important findings. MRI-related research was partly successful with the observation of the helical MRI  and the azimuthal MRI  at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). First evidence of the current-driven Tayler instability (TI) in a liquid metal was obtained here, too .
The lecture gives a cursory account of the recent laboratory experiments on dynamo action and magnetically triggered flow instabilities. It concludes with an overview about future experiments, with special focus on the precession-driven liquid sodium experiment and the large-scale MRI experiment that are under construction in the framework of the DRESDYN project at HZDR 
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