Contribution to Laboratory Astrophysics Workshop

[Hantao Ji <hji@princeton.edu>]

Dear Prof. Federman,

Thank you for sending me the preliminary announcement of the workshop,
I would like to contribute to your workshop, as encouraged by Dr.  
Hasan from
NASA. Our project is a laboratory experiment to study relevant  
astrophysical
processes for accretion disks. (Our website is http://mri.pppl.gov ).  
This project
belongs to part of Plasma Lab Astrophysics, currently partially  
funded by
NASA. The title of my presentation would be

"Laboratory Study of Magnetorotational Instability and Hydrodynamic  
Stability
at Larger Reynolds Numbers"

with an abstract attached below. Since we are new to this community,  
I would
appreciate it very much if this can be allocated as a contributed  
talk to expose
ourselves to a larger audience if all possible. Please let me know if  
you
need anything from me or any suggestions.

Best regards,

-Hantao
http://w3.pppl.gov/~hji

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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 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 with million Reynolds numbers,
casting questions on viability of the nonlinear hydrodynamic  
instability.
This project is supported by NASA, DoE, and NSF.