Astronomy and Astrophysics – Astronomy
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21641004t&link_type=abstract
American Astronomical Society, AAS Meeting #216, #410.04; Bulletin of the American Astronomical Society, Vol. 41, p.818
Astronomy and Astrophysics
Astronomy
Scientific paper
The observation of the dynamo effect in a simply connected turbulent system has yet to be observed in the laboratory without the use of highly ferromagnetic materials. In the Madison Dynamo Experiment, two counter-rotating impellers drive a turbulent flow of liquid sodium in a one meter-diameter sphere. Two main results have been discovered so far: first, no sustained self-excited field was seen, but intermittent bursts of a transverse dipole field similar to the induced field predicted by laminar kinematics were observed. Second, a weak, DC external seed field, sharing the symmetry axis of the mean flow, was applied to the flowing sodium. Data modeling showed that the currents measured in the sodium could not be explained from the mean flow alone. However, the overall trend was consistent with an enhanced resistivity (a beta effect). These experiments have demonstrated the need for a turbulent electromotive force to describe the dynamics of the magnetic field evolution. This poster will present efforts to optimize the flow in order to observe spontaneous magnetic field generation as well as methods to characterize the turbulent EMF. The addition of an equatorial and poloidal baffles to the experiment will help in the reduction of large-scale turbulence and optimization of the helicity of the mean flow. A high current H-bridge signal generator has been constructed to apply 500 Gauss, sinusoidal fields with frequencies up to 10 Hz. The profile of the response will be measured by an internal array of 3D hall probes. This profile should provide an indication of the turbulent enhancement to resistivity. The strengthened externally applied field will also be used to explore a sub-critical dynamo transition that has recently been discovered in numerical simulations.
Forest Cary B.
Kaplan E. J.
Kendrick R. D.
Nornberg Mark D.
Spence Erik J.
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