Helical magnetorotational instability in a liquid metal Taylor-Couette experiment

Cosmic magnetic fields are not only passive by-products of the hydromagnetic dynamo effect, they also play an active role in the formation of stars and black holes by virtue of the Magnetorotational Instability (MRI). By destabilizing Keplerian flows which are hydrodynamically stable due to Rayleighs criterion, the MRI enables outward transport of angular momentum in accretion discs. The effort to investigate the MRI in a liquid metal experiment can be dramatically reduced if the purely axial magnetic field is replaced by a helical magnetic field. We present results of a Taylor-Couette experiment with the liquid metallic alloy GaInSn under the influence of helical magnetic fields that show typical features of MRI at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10.