Liquid sodium flows showing the magnetorotational instability

You can now read the published PRL paper.

Diverse astrophysical phenomena involve the close interplay of rotation and magnetic fields. There is theoretical and computational evidence for the importance of small magnetic fields in destabilizing differential rotation: a process now often called the magnetorotational instability. This phenomena is invoked to explain how rotating clouds proceed to collapse in star formation. The instability leads to radial outflow of angular momentum, so that matter may fall inward instead of continuing to orbit. Magnetic fields in differentially rotating stars and planetary interiors are also thought to be affected. This research describes the first direct observation of this instability. The experimental device consists of liquid sodium confined between boundaries defined by a rotating inner sphere and a stationary outer sphere, with an imposed coaxial magnetic field. We characterize an array of observed patterns and dynamics in a saturated magnetorotational state and relate these observations to theoretical expectations.

Measurements of the induced field allow us to produce detailed movies of the dynamics of the magnetorotational instability (here for a m=1 state).

At higher appied field we see many different patterns, including m=0 states which remind one of the zonal flows on giant planets.

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