A model of nonlinear evolution and saturation of the turbulent MHD dynamo

The growth and saturation of magnetic field in conducting turbulent media with large magnetic Prandtl numbers are investigated. This regime is very common in low-density hot astrophysical plasmas. During the early (kinematic) stage, weak magnetic fluctuations grow exponentially and concentrate at th...

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Main Authors: Schekochihin, A, Cowley, S, Hammett, G, Maron, J, McWilliams, J
Format: Journal article
Language:English
Published: IOP Publishing 2002
_version_ 1797103663707062272
author Schekochihin, A
Cowley, S
Hammett, G
Maron, J
McWilliams, J
author_facet Schekochihin, A
Cowley, S
Hammett, G
Maron, J
McWilliams, J
author_sort Schekochihin, A
collection OXFORD
description The growth and saturation of magnetic field in conducting turbulent media with large magnetic Prandtl numbers are investigated. This regime is very common in low-density hot astrophysical plasmas. During the early (kinematic) stage, weak magnetic fluctuations grow exponentially and concentrate at the resistive scale, which lies far below the hydrodynamic viscous scale. The evolution becomes nonlinear when the magnetic energy is comparable to the kinetic energy of the viscous-scale eddies. A physical picture of the ensuing nonlinear evolution of the MHD dynamo is proposed. Phenomenological considerations are supplemented with a simple Fokker-Planck model of the nonlinear evolution of the magnetic-energy spectrum. It is found that, while the shift of the bulk of the magnetic energy from the subviscous scales to the velocity scales may be possible, it occurs very slowly - at the resistive, rather than dynamical, timescale (for galaxies, this means that the generation of large-scale magnetic fields cannot be explained by this mechanism). The role of Alfvénic motions and the implications for the fully developed isotropic MHD turbulence are discussed.
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spelling oxford-uuid:f36559c0-0618-44ad-aed6-1f9e9da4beaf2022-03-27T12:11:55ZA model of nonlinear evolution and saturation of the turbulent MHD dynamoJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:f36559c0-0618-44ad-aed6-1f9e9da4beafEnglishSymplectic Elements at OxfordIOP Publishing2002Schekochihin, ACowley, SHammett, GMaron, JMcWilliams, JThe growth and saturation of magnetic field in conducting turbulent media with large magnetic Prandtl numbers are investigated. This regime is very common in low-density hot astrophysical plasmas. During the early (kinematic) stage, weak magnetic fluctuations grow exponentially and concentrate at the resistive scale, which lies far below the hydrodynamic viscous scale. The evolution becomes nonlinear when the magnetic energy is comparable to the kinetic energy of the viscous-scale eddies. A physical picture of the ensuing nonlinear evolution of the MHD dynamo is proposed. Phenomenological considerations are supplemented with a simple Fokker-Planck model of the nonlinear evolution of the magnetic-energy spectrum. It is found that, while the shift of the bulk of the magnetic energy from the subviscous scales to the velocity scales may be possible, it occurs very slowly - at the resistive, rather than dynamical, timescale (for galaxies, this means that the generation of large-scale magnetic fields cannot be explained by this mechanism). The role of Alfvénic motions and the implications for the fully developed isotropic MHD turbulence are discussed.
spellingShingle Schekochihin, A
Cowley, S
Hammett, G
Maron, J
McWilliams, J
A model of nonlinear evolution and saturation of the turbulent MHD dynamo
title A model of nonlinear evolution and saturation of the turbulent MHD dynamo
title_full A model of nonlinear evolution and saturation of the turbulent MHD dynamo
title_fullStr A model of nonlinear evolution and saturation of the turbulent MHD dynamo
title_full_unstemmed A model of nonlinear evolution and saturation of the turbulent MHD dynamo
title_short A model of nonlinear evolution and saturation of the turbulent MHD dynamo
title_sort model of nonlinear evolution and saturation of the turbulent mhd dynamo
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