Experiments in Magnetohydrodynamic and Hydrodynamic Instabilities of Astrophysical Interest

Princeton University, Princeton NJ

Investigators

Abstract

Efficient dissipation of the orbital energy of plasma occurs in accretion disks ranging from those in which planets form around protostars, to those around supermassive black holes in active galactic nuclei. Two mechanisms have been proposed for the turbulence that drives dissipation and angular-momentum transport in such disks: (1) a linear instability of magnetized and electrically conducting flow known as magnetorotational instability (MRI); and (2) nonlinear hydrodynamic shear-flow instability. Two experiments are running at Princeton: the Liquid-Metal experiment studies MRI and related magnetohydrodynamic (MHD) instabilities, while the Hydrodynamic Turbulence Experiment studies nonlinear hydrodynamic transitions. Recently, the MHD experiment has demonstrated robust nonaxisymmetric Shercliff-layer instabilities in strong axial magnetic fields, paving a clear path towards a first conclusive demonstration of MRI in the laboratory. The present contribution to this research will focus on experimental studies of the following questions: (1) Why are quasi-keplerian flows resistant to turbulence? and (2) How do MRI, Shercliff-layer instabilities, and other MHD activity, drive angular momentum transport? This requires adding crucial diagnostics for direct global torque measurements, measuring local Reynolds and Maxwell stresses in the liquid-metal flow; and making critical hardware improvements to increase and control rotation speeds. This research will educate the next generation of scientists and forge links with neighboring disciplines such as geophysics, fluid dynamics, and plasma physics, while advancing laboratory astrophysics generally.