Kiel 2011 – wissenschaftliches Programm
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P: Fachverband Plasmaphysik
P 13: Astrophysikalische Plasmen
P 13.4: Fachvortrag
Mittwoch, 30. März 2011, 11:30–11:55, HS C
The role of system-scale turbulence on MHD activity in a spherical dynamo experiment — •Kian Rahbarnia1, Mike M Clark1, Elliot J Kaplan1, Mark D Nornberg1, Alex M Rasmus1, Eric J Spence2, Nicholas Z Taylor1, John P Wallace1, and Cary B Forest1 — 1Department of Physics, University of Wisconsin-Madison, 53706 Madison,WI, USA — 2Princeton Plasma Physics Laboratory, New Jersey 08544, USA
Self-generation and saturation of magnetic fields due to magnetohydrodynamic (MHD) dynamos remain important fundamental problems in many astrophysical and geophysical systems. The Madison Dynamo Experiment (MDE) studies the onset conditions for magnetic field growth in a turbulent flow of liquid sodium and investigates the turbulent electromotive force ε=⟨ṽ × b̃ ⟩. This work analyzes the influence of a recently installed equatorial baffle to reduce the largest scale turbulent eddies in the flow. A spherical harmonic decomposition of the magnetic field indicates a reduction of the largest scale magnetic fluctuations, consistent with a reduction of the large-scale velocity fluctuations. With the baffle the amplification of a transverse seed magnetic field (expected dynamo eigenmode) shows a gain of about 40% and increasing decay times with Reynolds number. This may also indicate a reduction of the turbulent resistivity. For the first time in the MDE the local ε is experimentally observed by measuring velocity and magnetic fluctuations simultaneously at specific positions in the liquid sodium. This work is supported by the CMSO and the NSF/DOE partnership in plasma physics.