Driving large magnetic Reynolds number flow in highly ionized, unmagnetized plasmas

Electrically driven, unmagnetized plasma flows have been generated in the Madison plasma dynamo experiment with magnetic Reynolds numbers exceeding the predicted Rmcrit  = 200 threshold for flow-driven MHD instability excitation. The plasma flow is driven using ten thermally emissive lanthanum hexab...

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Bibliographic Details
Published in:Physics of plasmas 2017-05, Vol.24 (5)
Main Authors: Weisberg, D. B., Peterson, E., Milhone, J., Endrizzi, D., Cooper, C., Désangles, V., Khalzov, I., Siller, R., Forest, C. B.
Format: Article
Language:English
Subjects:
Drag
Flow stability
Fluid dynamics
Fluid flow
Helium
Lanthanum
Magnetohydrodynamics
Plasma physics
Plasmas (physics)
Radial velocity
Reynolds number
Transport theory
Velocity
Velocity distribution
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Summary:Electrically driven, unmagnetized plasma flows have been generated in the Madison plasma dynamo experiment with magnetic Reynolds numbers exceeding the predicted Rmcrit  = 200 threshold for flow-driven MHD instability excitation. The plasma flow is driven using ten thermally emissive lanthanum hexaboride cathodes which generate a J × B torque in helium and argon plasmas. Detailed Mach probe measurements of plasma velocity for two flow topologies are presented: edge-localized drive using the multi-cusp boundary field and volumetric drive using an axial Helmholtz field. Radial velocity profiles show that the edge-driven flow is established via ion viscosity but is limited by a volumetric neutral drag force, and measurements of velocity shear compare favorably to the Braginskii transport theory. Volumetric flow drive is shown to produce larger velocity shear and has the correct flow profile for studying the magnetorotational instability.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4978889