Dynamo action, magnetorotational instability, Alfvén waves: Theory and experiments on astrophysical magnetohydrodynamics

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• Frank Stefani (Helmholtz-Zentrum Dresden)
• Monday 05 February 2024, 14:00-15:00
• MR14 DAMTP and online.

If you have a question about this talk, please contact Roger Dufresne.

The homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas, is responsible for magnetic-field generation in planets, stars and galaxies. Magnetic fields, in turn, can promote cosmic structure formation by destabilizing, via the magnetorotational instability (MRI), rotational flows in accretion disks that otherwise would be hydrodynamically stable.

For a long time, those topics have been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was crossed in two large-scale liquid-sodium experiments in Riga and Karlsruhe. Later, the VKS dynamo experiment in Cadarache successfully reproduced field reversals and excursions that are of great geophysical interest. Various types of the MRI were studied in liquid metal experiments at the Princeton Plasma Physics Laboratory and at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid-rubidium experiment at the Dresden High Magnetic Field Laboratory (HLD) reached the “magic point” of coinciding Alfvén and sound speeds, which is thought to play a key role for the heating of the solar corona.

After a short introduction to the basic equations of magnetohydrodynamics, the lecture gives an overview about previous and future liquid metal experiments on dynamo action, Alfvén waves, and magnetically triggered flow instabilities such as the MRI . Special focus lies on a precession driven dynamo experiment that is presently being constructed in frame of the DRESDYN project at HZDR . Closely related to this, some emphasis is placed on the potential role of various astronomical forcings in triggering reversals of the geodynamo or even synchronizing the solar dynamo.

This talk is part of the DAMTP Astrophysics Seminars series.

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