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Title: Optimization of magnetic amplification by flow constraints in turbulent liquid sodium

Direct measurements of the vector turbulent emf in a driven two-vortex flow of liquid sodium were performed in the Madison Dynamo Experiment [K. Rahbarnia et al., Astrophys. J. 759, 80 (2012)]. The measured turbulent emf is anti-parallel with the mean current and is almost entirely described by an enhanced resistivity, which increases the threshold for a kinematic dynamo. We have demonstrated that this enhanced resistivity can be mitigated by eliminating the largest-scale eddies through the introduction of baffles. By tailoring the flow to reduce large-scale components and control the helical pitch, we have reduced the power required to drive the impellers, doubled the magnetic flux generated by differential rotation, and increased the decay time of externally applied magnetic fields. Despite these improvements, the flows remain sub-critical to the dynamo instability due to the reemergence of turbulent fluctuations at high flow speeds.
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Center for Magnetic-Self Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States)
  2. Max-Planck-Institut fur Plasmaphysik Wendelsteinstra├če 1, D-17491 Greifswald (Germany)
  3. Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany)
Publication Date:
OSTI Identifier:
22252904
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BAFFLES; CONTROL; ELECTROMOTIVE FORCE; FLUCTUATIONS; LIMITING VALUES; LIQUIDS; MAGNETIC FIELDS; MAGNETIC FLUX; OPTIMIZATION; PITCHES; SODIUM