It has long been assumed that turbulent angular momentum transport is a driving force explaining why accretion disks accrete, simply because such disks have very large Reynolds numbers (Re). Theoretical and numerical studies have shown that magneto-rotational instabilities (MRI) can support vigorous turbulence, so that MRI is now the favored mechanism for accretion in disks ranging from quasars to cataclysmic variables. However, MRI requires sufficient ionization to provide good electrical conductivity, which cool disks may not provide, so hydrodynamic turbulence is sometimes invoked. This project is an experimental laboratory study of high-Re MRI in liquid metal, to demonstrate MRI and study its nonlinear behavior, to investigate the stability of hydrodynamic flows at large Re, and to compare the laboratory results quantitatively with simulated astrophysical disks. These comparisons will help to validate theoretical tools applicable to nonlinear saturation of resistive MRI in astrophysical systems, especially proto-stellar disks.
Success will require the combined efforts of experimental physicists, computational fluid-dynamicists, and theoretical astrophysicists, who have much to learn from one another. Student training will be particularly valuable, since the field of experimental astrophysics is still rather small.
