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Laboratory experiments on dynamo action and magnetically triggered flow instabilities

Stefani, F.

Magnetic fields of planets, stars and galaxies are known to be generated 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) or the Tayler instability (TI), those rotating flows that would be otherwise hydrodynamically stable. The mutual reinforcement of dynamo action and magnetic instabilities leads to interesting concepts such as the MRI-dynamo or the Tayler-Spruit-dynamo.
For a long time, all these topics had been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded 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 reversals and excursions. Further liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, and Socorro have contributed important findings related to the alpha, beta and Omega effects as well as to various wave phenomena in magnetized rotating fluids. MRI-related research was partly successful with the observation of the helical MRI and the azimuthal MRI at the PROMISE facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). First evidence of the current-driven Tayler instability in a liquid metal was also obtained.
The lecture gives an overview about liquid metal 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 Tayler-Couette experiment that are under construction in the framework of the DRESDYN project at HZDR.The prospects for experimental validation of the recently discussed magnetic destabilization of flows with positive shear are also discussed.

  • Invited lecture (Conferences)
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice, Czech Republic

Publ.-Id: 25812