A Spherical Plasma Dynamo Experiment

Spence, E. J.; Reuter, Klaus; Forest, C. B.

doi:10.1088/0004-637x/700/1/470

Cited by 35 publications

(48 citation statements)

References 52 publications

(54 reference statements)

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“…Besides being of astrophysical (origin of observed fields) and fundamental (what happens?) physical interest, it is likely soon to be attacked not just theoretically, but also experimentally, with the advent of laboratory experiments aiming to reproduce the plasma dynamo process (Spence et al 2009;Meinecke et al 2014Meinecke et al , 2015Plihon et al 2015;Forest et al 2015). The first demonstration of this process in a 3D kinetic numerical simulation by Rincon et al (2016) has indeed confirmed the ubiquitous appearance of mirror and firehose fluctuations, although a detailed investigation of the full multiscale problem remains computationally too intensive to be affordable.…”

Section: Introductionmentioning

confidence: 99%

Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma

Melville¹,

Schekochihin²,

Kunz³

2016

Mon. Not. R. Astron. Soc.

126

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The nonlinear state of a high-beta collisionless plasma is investigated in which an externally imposed linear shear amplifies or diminishes a uniform mean magnetic field, driving pressure anisotropies and, therefore, firehose or mirror instabilities. The evolution of the resulting microscale turbulence is considered when the external shear changes, mimicking the local behaviour of a macroscopic turbulent plasma flow, viz., the shear is either switched off or reversed after one shear time, so that a new macroscale configuration is superimposed on the microscale state left behind by the previous one. It is shown that there is a threshold value of plasma beta: when β ≪ Ω/S (ion cyclotron frequency/shear rate), the emergence of firehose or mirror fluctuations when they are driven unstable by shear and their disappearance when the shear is removed or reversed are quasi-instantaneous compared to the macroscopic (shear) timescale. This is because the free-decay time scale of these fluctuations is ∼ β/Ω ≪ S −1 , a result that arises from the free decay of both types of fluctuations turning out to be constrained by the same marginal-stability thresholds as their growth and saturation in the driven regime. In contrast, when β Ω/S ("ultra-high" beta), the old microscale state can only be removed on the macroscopic (shear) timescale. Furthermore, it is found that in this ultra-high-beta regime, when the firehose fluctuations are driven, they grow secularly to order-unity amplitudes (relative to the mean field), this growth compensating for the decay of the mean field, with pressure anisotropy pinned at marginal stability purely by the increase in the fluctuation energy, with no appreciable scattering of particles (which is unlike what happens at moderate β). When the shear reverses, the shearing away of this firehose turbulence compensates for the increase in the mean field and thus prevents growth of the pressure anisotropy, stopping the system from going mirror-unstable. Therefore, at ultra-high β, the system stays close to the firehose threshold, the mirror instability is almost completely suppressed, while the mean magnitude of the magnetic field barely changes at all. Implications of the properties of both ultra-high-and moderate-beta regimes for the operation of plasma dynamo and thus the origin of cosmic magnetism are discussed, suggesting that collisionless effects are broadly beneficial to fast magnetic-field generation.

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Section: Introductionmentioning

confidence: 99%

Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma

Melville¹,

Schekochihin²,

Kunz³

2016

Mon. Not. R. Astron. Soc.

126

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“…1,[3][4][5] The process for experimental design is briefly reviewed to both emphasize the connection between the dimensionless parameters used in the modeling but also to illustrate how the experiments are planned to operate. The essence of the stirring is that the axisymmetric multi-cusp magnetic field and cathode stirring allow the azimuthal velocity profile (rotation) v / ðh; tÞ to be controlled at the plasma boundary.…”

Section: A Dynamo Scenariosmentioning

confidence: 99%

“…Such a device accesses a new regime relevant to astrophysical applications and never before achieved in a laboratory. 1 This plasma is well-suited for studying astrophysical phenomena such as the dynamo process, 2 the feasibility of which is the topic of several recent publications [3][4][5] and is investigated in Sec. IV A.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic plasma research device designed to investigate flow driven magnetohydrodynamic instabilities and other high-b 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 3 of nearly magnetic field free plasma that is well confined and highly ionized (>50%). At present, 8 lanthanum hexaboride (LaB 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 6 cathodes are positioned in the magnetized edge to drive toroidal rotation through J Â 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 2 A ¼ ðv=v A Þ 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. V C 2014 AIP Publishing LLC.

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“…There is a clear scientific opportunity to operate a plasma physics dynamo experiment exploring very high beta plasma physics in which a fast flowing, hot plasma is confined in a largely magnetic field free volume, as depicted in Figure 12 [46]. This opportunity builds upon the excitement in recent years of using liquid metals to study dynamos, and will extend these studies to more astrophysically relevant parameters.…”

Section: Line-tied Magnetic Reconnection and Magnetic Dynamo Researchmentioning

confidence: 99%

Exploiting Laboratory and Heliophysics Plasma Synergies

et al. 2010

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Recent advances in space-based heliospheric observations, laboratory experimentation, and plasma simulation codes are creating an exciting new cross-disciplinary opportunity for understanding fast energy release and transport mechanisms in heliophysics and laboratory plasma dynamics, which had not been previously accessible. This article provides an overview of some new observational, experimental, and computational assets, and discusses current and near-term activities towards exploitation of synergies involving those assets. This overview does not claim to be comprehensive, but instead covers mainly activities closely associated with the authors' interests and reearch. Heliospheric observations reviewed include the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) on the National Aeronautics and Space Administration (NASA) Solar Terrestrial Relations Observatory (STEREO) mission, the first instrument to provide remote sensing imagery observations with spatial continuity extending from the Sun to the Earth, and the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Japanese Hinode spacecraft that is measuring spectroscopically OPEN ACCESSEnergies 2010, 3 1015 physical parameters of the solar atmosphere towards obtaining plasma temperatures, densities, and mass motions. The Solar Dynamics Observatory (SDO) and the upcoming Solar Orbiter with the Heliospheric Imager (SoloHI) on-board will also be discussed. Laboratory plasma experiments surveyed include the line-tied magnetic reconnection experiments at University of Wisconsin (relevant to coronal heating magnetic flux tube observations and simulations), and a dynamo facility under construction there; the Space Plasma Simulation Chamber at the Naval Research Laboratory that currently produces plasmas scalable to ionospheric and magnetospheric conditions and in the future also will be suited to study the physics of the solar corona; the Versatile Toroidal Facility at the Massachusetts Institute of Technology that provides direct experimental observation of reconnection dynamics; and the Swarthmore Spheromak Experiment, which provides well-diagnosed data on three-dimensional (3D) null-point magnetic reconnection that is also applicable to solar active regions embedded in pre-existing coronal fields. New computer capabilities highlighted include: HYPERION, a fully compressible 3D magnetohydrodynamics (MHD) code with radiation transport and thermal conduction; ORBIT-RF, a 4D Monte-Carlo code for the study of wave interactions with fast ions embedded in background MHD plasmas; the 3D implicit multi-fluid MHD spectral element code, HiFi; and, the 3D Hall MHD code VooDoo. Research synergies for these new tools are primarily in the areas of magnetic reconnection, plasma charged particle acceleration, plasma wave propagation and turbulence in a diverging magnetic field, plasma atomic processes, and magnetic dynamo behavior.

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A Spherical Plasma Dynamo Experiment

Cited by 35 publications

References 52 publications

Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma

Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma

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

Exploiting Laboratory and Heliophysics Plasma Synergies

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