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Title: The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics

Abstract

The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic plasma research device designed to investigate flow driven magnetohydrodynamic instabilities and other high-β phenomena with astrophysically relevant parameters. A 3 m diameter vacuum vessel is lined with 36 rings of alternately oriented 4000 G samarium cobalt magnets, which create an axisymmetric multicusp that contains ∼14 m{sup 3} of nearly magnetic field free plasma that is well confined and highly ionized (>50%). At present, 8 lanthanum hexaboride (LaB{sub 6}) cathodes and 10 molybdenum anodes are inserted into the vessel and biased up to 500 V, drawing 40 A each cathode, ionizing a low pressure Ar or He fill gas and heating it. Up to 100 kW of electron cyclotron heating power is planned for additional electron heating. The LaB{sub 6} cathodes are positioned in the magnetized edge to drive toroidal rotation through J × B torques that propagate into the unmagnetized core plasma. Dynamo studies on MPDX require a high magnetic Reynolds number Rm > 1000, and an adjustable fluid Reynolds number 10 < Re < 1000, in the regime where the kinetic energy of the flow exceeds the magnetic energy (M{sub A}{sup 2}=(v/v{sub A}){sup 2}>1). Initial results from MPDX are presented along with a 0-dimensional power and particle balance model to predictmore » the viscosity and resistivity to achieve dynamo action.« less

Authors:
; ; ; ; ; ; ;  [1];  [2]; ; ; ; ;  [1];  [3];  [4];  [1];  [2];  [2]
  1. Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)
  2. (United States)
  3. Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90024 (United States)
  4. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
Publication Date:
OSTI Identifier:
22252165
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 1; 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; ANODES; ASTROPHYSICS; CATHODES; ECR HEATING; LANTHANUM BORIDES; MAGNETIC FIELDS; MAGNETIC REYNOLDS NUMBER; MAGNETS; MOLYBDENUM; PLASMA; SAMARIUM

Citation Formats

Cooper, C. M., Brookhart, M., Collins, C., Khalzov, I., Milhone, J., Nornberg, M., Weisberg, D., Forest, C. B., Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706, Wallace, J., Clark, M., Flanagan, K., Li, Y., Nonn, P., Ding, W. X., Whyte, D. G., Zweibel, E., Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706, and Department of Astronomy, University of Wisconsin, Madison, Wisconsin 53706. The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics. United States: N. p., 2014. Web. doi:10.1063/1.4861609.
Cooper, C. M., Brookhart, M., Collins, C., Khalzov, I., Milhone, J., Nornberg, M., Weisberg, D., Forest, C. B., Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706, Wallace, J., Clark, M., Flanagan, K., Li, Y., Nonn, P., Ding, W. X., Whyte, D. G., Zweibel, E., Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706, & Department of Astronomy, University of Wisconsin, Madison, Wisconsin 53706. The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics. United States. doi:10.1063/1.4861609.
Cooper, C. M., Brookhart, M., Collins, C., Khalzov, I., Milhone, J., Nornberg, M., Weisberg, D., Forest, C. B., Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706, Wallace, J., Clark, M., Flanagan, K., Li, Y., Nonn, P., Ding, W. X., Whyte, D. G., Zweibel, E., Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706, and Department of Astronomy, University of Wisconsin, Madison, Wisconsin 53706. Wed . "The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics". United States. doi:10.1063/1.4861609.
@article{osti_22252165,
title = {The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics},
author = {Cooper, C. M. and Brookhart, M. and Collins, C. and Khalzov, I. and Milhone, J. and Nornberg, M. and Weisberg, D. and Forest, C. B. and Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706 and Wallace, J. and Clark, M. and Flanagan, K. and Li, Y. and Nonn, P. and Ding, W. X. and Whyte, D. G. and Zweibel, E. and Center for Magnetic Self Organization, University of Wisconsin, Madison, Wisconsin 53706 and Department of Astronomy, University of Wisconsin, Madison, Wisconsin 53706},
abstractNote = {The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic plasma research device designed to investigate flow driven magnetohydrodynamic instabilities and other high-β phenomena with astrophysically relevant parameters. A 3 m diameter vacuum vessel is lined with 36 rings of alternately oriented 4000 G samarium cobalt magnets, which create an axisymmetric multicusp that contains ∼14 m{sup 3} of nearly magnetic field free plasma that is well confined and highly ionized (>50%). At present, 8 lanthanum hexaboride (LaB{sub 6}) cathodes and 10 molybdenum anodes are inserted into the vessel and biased up to 500 V, drawing 40 A each cathode, ionizing a low pressure Ar or He fill gas and heating it. Up to 100 kW of electron cyclotron heating power is planned for additional electron heating. The LaB{sub 6} cathodes are positioned in the magnetized edge to drive toroidal rotation through J × B torques that propagate into the unmagnetized core plasma. Dynamo studies on MPDX require a high magnetic Reynolds number Rm > 1000, and an adjustable fluid Reynolds number 10 < Re < 1000, in the regime where the kinetic energy of the flow exceeds the magnetic energy (M{sub A}{sup 2}=(v/v{sub A}){sup 2}>1). Initial results from MPDX are presented along with a 0-dimensional power and particle balance model to predict the viscosity and resistivity to achieve dynamo action.},
doi = {10.1063/1.4861609},
journal = {Physics of Plasmas},
number = 1,
volume = 21,
place = {United States},
year = {Wed Jan 15 00:00:00 EST 2014},
month = {Wed Jan 15 00:00:00 EST 2014}
}
  • Turbulent fluctuations in the velocity and magnetic fields of electrically conducting fluids have been experimentally shown to be capable of inducing large-scale magnetic fields. Here, simulations of the Madison Dynamo Experiment are used to qualitatively reproduce these experimental results. Due to the high magnetic Prandtl number of the simulations, Pm=0.08 vs Pm{approx}10{sup -5} for liquid sodium, the simulations do not identically reproduce the fluctuation levels of the experiment's magnetic and velocity fields. Nonetheless, the simulations reproduce the qualitative behavior of the fluctuation-induced large-scale magnetic field as a function of applied field magnitude and magnetic Reynolds number. The scaling of themore » induced dipole moment as a function of Reynolds number is also presented, demonstrating that the nature of the fluctuations in the simulations changes after a critical value of the Reynolds number is crossed, resulting in a change in the direction of the induced dipole moment. Experimental conditions using corotating impellers are presented, demonstrating that the induced dipole moment may be dependent on the shear layer present in the counter-rotating case. Measurements of velocity field fluctuations are examined to determine the possibility of an inhomogeneous turbulent resistivity.« less
  • The Euler similarity criteria for laboratory experiments and time-dependent mixing transition are important concepts introduced recently for application to prediction and analysis of astrophysical phenomena. However Euler scaling by itself provides no information on the distinctive spectral range of high Reynolds number turbulent flows found in astrophysics situations. On the other hand, time-dependent mixing transition gives no indication on whether a flow that just passed the mixing transition is sufficient to capture all of the significant dynamics of the complete astrophysical spectral range. In this paper, a new approach, based on additional insight gained from review of Navier-Stokes turbulence theory,more » is developed. It allows for revelations about the distinctive spectral scale dynamics associated with high Reynolds number astrophysical flows. From this perspective, we caution that the energy containing range of the turbulent flow measured in a laboratory setting must not be unintentionally contaminated in such a way that the interactive influences of this spectral scale range in the corresponding astrophysical situation cannot be faithfully represented. In this paper we introduce the concept of a minimum state as the lowest Reynolds number turbulent flow that a time-dependent mixing transition must achieve to fulfill this objective. Later in the paper we show that the Reynolds number of the minimum state may be determined as 1.6 x 10{sup 5}. Our efforts here can be viewed as a unification and extension of the concepts of both similarity scaling and transient mixing transition concepts. At the last the implications of our approach in planning future intensive laser experiments or massively parallel numerical simulations are discussed. A systematic procedure is outlined so that as the capabilities of the laser interaction experiments and supporting results from detailed numerical simulations performed in recently advanced supercomputing facilities increase progressively, a strategy can be devised so that more and more spectral range dynamic structures and their statistical influences on evolving astrophysical flows can be progressively extended in laboratory investigations.« less
  • The Euler similarity criteria for laboratory experiments and time-dependent mixing transition are important concepts introduced recently for application to prediction and analysis of astrophysical phenomena. However, Euler scaling by itself provides no information on the distinctive spectral range of high Reynolds number turbulent flows found in astrophysics situations. On the other hand, time-dependent mixing transition gives no indication on whether a flow that just passed the mixing transition is sufficient to capture all of the significant dynamics of the complete astrophysical spectral range. In this paper, a new approach, based on additional insight gained from review of Navier-Stokes turbulence theory,more » is developed. It allows for revelations about the distinctive spectral scale dynamics associated with high Reynolds number astrophysical flows. From this perspective, the energy-containing range of the turbulent flow measured in a laboratory setting must not be unintentionally contaminated in such a way that the interactive influences of this spectral scale range in the corresponding astrophysical situation cannot be faithfully represented. In this paper, the concept of a minimum state is introduced as the lowest Reynolds number turbulent flow that a time-dependent mixing transition must achieve to fulfill this objective. Later in the paper, the Reynolds number of the minimum state is determined as 1.6x10{sup 5}. The temporal criterion for the minimum state is also obtained. The efforts here can be viewed as a unification and extension of the concepts of both similarity scaling and transient mixing transition concepts. Finally, the implications of our approach in planning future intensive laser experiments or massively parallel numerical simulations are discussed. A systematic procedure is outlined so that as the capabilities of the laser interaction experiments and supporting results from detailed numerical simulations performed in recently advanced supercomputing facilities increase progressively, a strategy is developed so that a progressively increasing range of dynamic structures and their statistical influences on evolving astrophysical flows can be attained in laboratory investigations.« less
  • The scientific equipment purchased on this grant was used on the Plasma Dynamo Prototype Experiment as part of Professor Forest's feasibility study for determining if it would be worthwhile to propose building a larger plasma physics experiment to investigate various fundamental processes in plasma astrophysics. The initial research on the Plasma Dynamo Prototype Experiment was successful so Professor Forest and Professor Ellen Zweibel at UW-Madison submitted an NSF Major Research Instrumentation proposal titled "ARRA MRI: Development of a Plasma Dynamo Facility for Experimental Investigations of Fundamental Processes in Plasma Astrophysics." They received funding for this project and the Plasma Dynamomore » Facility also known as the "Madison Plasma Dynamo Experiment" was constructed. This experiment achieved its first plasma in the fall of 2012 and U.S. Dept. of Energy Grant No. DE-SC0008709 "Experimental Studies of Plasma Dynamos," now supports the research.« less
  • We propose a plasma experiment to be used to investigate fundamental properties of astrophysical dynamos. The highly conducting, fast-flowing plasma will allow experimenters to explore systems with magnetic Reynolds numbers an order of magnitude larger than those accessible with liquid-metal experiments. The plasma is confined using a ring-cusp strategy and subject to a toroidal differentially rotating outer boundary condition. As proof of principle, we present magnetohydrodynamic simulations of the proposed experiment. When a von Karman-type boundary condition is specified, and the magnetic Reynolds number is large enough, dynamo action is observed. At different values of the magnetic Prandtl and Reynoldsmore » numbers the simulations demonstrate either laminar or turbulent dynamo action.« less