The Magnetorotational Instability: Experimental characterization of electric currents in hydromagnetic Taylor-Couette flows

Abstract

The precise mechanics of matter and angular momentum transport in accretion disks around astronomical bodies are not yet fully understood. One of the processes involved is the magnetorotational instability (MRI), which under the right circumstances can result in turbulence-enhanced viscosity in magnetized fluids. MRI is a direct prediction of magnetohydrodynamic (MHD) models typically involved in the study of plasmas, both astronomical and fusion-oriented, and there exist various numerical simulations that match observations of accretion disks. However, the MRI has not been explored to its full extent in the laboratory. Previous experiments at the Princeton Plasma Physics Laboratory have utilized a Taylor-Couette device to impart a differential angular velocity to a magnetized fluid, using nonconductive boundaries. In the current experiment, we explore the effects of conductive boundaries in the MRI machine. Specifically, there exist unexplained torques in the machine, which are conjectured to be a result of Lorentz forces arising from currents in the fluid. In this thesis, I present a method to characterize and measure these currents via the ideal MHD resistive Ohm’s Law. Results from this experiment confirm that there are currents present in the machine responsible for the observed torques. They are, however, only partially explained by the aforementioned law, so further study is necessary to fully characterize them. Ultimately, I offer suggestions for future investigation on the appearance and behavior of these currents.