Overview of the Princeton MagnetoRotational Instability Experiment

A turbulent viscosity is required to explain the observationally-inferred rates of angular momentum transport in accretion disks. Investigation of thin disks has focused on two sources of instability to drive the turbulence: the MagnetoRotational Instability (MRI) and Subcritical Hydrodynamic Instability (SHI). In MRI a weak ambient magnetic field causes the radially-decreasing angular velocity to become a source of free energy. In SHI, stable perturbations allow access to unstable modes. This experiment investigates both of these instabilities in a Couette-Taylor flow. Using water or liquid Gallium alloy we generate rotating shear flows with linear stability properties analagous to astrophysical disks. Differentially rotatable end-rings reduce boundary effects. We found no evidence of SHI, up to Reynolds number of order one million. During the MHD experiments a solenoidal magnetic field of up to 5~kG is applied. Radially-aligned induction coils detect magnetic perturbations generated by the liquid metal. Initial magnetized experiments focussed on magneto-Coriolis waves which at large magnetic Reynolds number are expected to transition into MRI modes. Results of the current search for the MRI will be presented.