A spherical Couette experiment to observe linear MHD instabilities at medium Reynolds numbers

Turbulent spherical Couette flows in a strong axial magnetic field (Re $\in (10^4, 10^6)$, Ha $\in (0,3000)$) have given rise to a nonaxisymmetric instability that resembled the long sought-after, nonlinear, Magnetorotational Instability [Sisan (2004)]. Subsequent theoretical and numerical investigations have likened the observed instability to linear instabilities in either the Shercliff layer or the return flow [Hollerbach (2009), Gissinger (2011)]. These investigations also turned up a stability region in Re/Ha space between these (MHD) instabilities and the (HD) jet instability. Presented here are designs and plans for a spherical Couette experiment---presently under construction in Rossendorf---that aims to measure these instablities in the space betwixt the simulations and the turbulent experiments (Re $\in (10^3,10^4)$, Ha $\in (0,160)$).