Initial results from the Princeton Magnetorotational Instability Experiment using liquid metal

The Magnetorotational Instability (MRI) is regarded as the dominant mechanism for accretion disk turbulence and its associated angular momentum transport. A series of experiments using both water and liquid metal in a novel wide-gap Taylor-Couette apparatus are conducted to elucidate the relative importance of sub-critical hydrodynamic turbulence to the MRI. Reynolds stress measurements using two-component laser Doppler velocimetry in water demonstrate that keplerian-like flows have extremely weak angular momentum transport even at Reynolds numbers up to $10^6$ when end effects are suppressed by differentially rotating end caps. By switching the working fluid to a liquid Gallium alloy (Ga-In-Sn), this quiescent flow can be destabilized by applying an axial magnetic field of up to 5~kG. The growth rate of the MRI is determined from external magnetic field measurements using radially-aligned induction coils and Hall probes. Secondary circulation induced by the MRI, which is a local instability, is distinguished experimentally from magnetically-induced Ekman circulation generated by the boundary layers through comparisons between flows which are stable and unstable to the MRI. This work is supported by DOE, NASA, and NSF.