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Fluid Dynamics Seminar


Monday, March 27th, 2006, 11:30 AM
Cullimore Lecture Hall, Room 611
New Jersey Institute of Technology

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Laboratory Astrophysics: Hydrodynamic Results from Princeton Magnetorotational Instability Experiment


Hantao Ji

 

Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, Princeton Plasma Physics Laboratory, Princeton University



Abstract

 

Rapid angular momentum transport in accretion disks has been a longstanding astrophysical puzzle. Molecular viscosity is inadequate to explain observationally inferred accretion rates. Since Keplerian flow profiles are linearly stable in hydrodynamics, there exist only two viable mechanisms for the required turbulence: nonlinear hydrodynamic instability or magnetohydrodynamic instability. The latter, also know as magnetorotational instability (MRI), is regarded as a dominant mechanism for rapid angular momentum transport in hot accretion disks ranging from quasars and X-ray binaries to cataclysmic variables. The former has been proposed mainly for colder protoplanetary disks, whose Reynolds numbers are typically large. Despite their popularity, however, both candidate mechanisms have been rarely demonstrated and studied in the laboratory. In this talk, I will describe initial results from a laboratory experiment in a short Taylor-Couette flow geometry ongoing at Princeton intended for such purposes. Based on the knowledge leant through prototype experiments and simulations, the apparatus contains novel features for better controls of the boundary-driven secondary flows (Ekman circulation). Initial results on hydrodynamic stability have shown, somewhat surprisingly, robust quiescence of the Keplerian-like flows and minimal angular momentum transport with million Reynolds numbers, casting questions on viability of the nonlinear hydrodynamic instability. Time permitting, another experiment on free-surface MHD flows will be briefly described. Both projects are supported by U.S. DoE, NSF, and NASA.