  Magnetic fields of planets, stars and galaxies are generated by
self-excitation in moving electrically conducting fluids. Once produced,
magnetic fields can play an active role in cosmic structure formation by
destabilizing rotational flows that would be otherwise hydrodynamically stable.
For a long time, both hydromagnetic dynamo action as well as magnetically
triggered flow instabilities had been the subject of purely theoretical
research. Meanwhile, however, the dynamo effect has been observed in
large-scale liquid sodium experiments in Riga, Karlsruhe and Cadarache. In this
paper, we summarize the results of some smaller liquid metal experiments
devoted to various magnetic instabilities such as the helical and the azimuthal
magnetorotational instability, the Tayler instability, and the different
instabilities that appear in a magnetized spherical Couette flow. We conclude
with an outlook on a large scale Tayler-Couette experiment using liquid sodium,
and on the prospects to observe magnetically triggered instabilities of flows
with positive shear.
