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Graduate Student Seminar - 04/27/2012

"Magnetic Instabilities in Turbulent Spherical Couette Flow"

by Matthew Adams

Friday, April 27, 2012 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor Daniel Lathrop

We present experimental studies of the turbulent flow of a conducting fluid in a spherical shear flow in the presence of a magnetic field. Our experimental apparatus consists of an outer spherical shell concentric with an inner sphere, each of which can be rotated independently, with liquid sodium filling the gap between them. The geometry of the experiment makes these studies relevant to geophysical and astrophysical bodies. We apply an axial magnetic field and measure the induced magnetic field around the device to obtain information about the global fluid flow. We also measure the torque required to drive the inner and outer spheres at their respective rotation rates. We study how the required torques change with the rotation rate ratio of the two spheres and with the strength of the applied magnetic field. For the inner sphere rotating faster than the outer sphere, we observe enhanced angular momentum transport as the applied field strength is increased for a variety of rotation rate ratios and we compare the observed magnetic field pattern with the expected magnetic instabilities. Of particular interest is the so-called magnetorotational instability (MRI), which is of importance in accretion disk dynamics.

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