Mechanism for sequestering magnetic energy at large scales in shear-flow turbulence

Straining of magnetic fields by large-scale shear flow, which is generally assumed to lead to intensification and generation of small scales, is reexamined in light of the persistent observation of large-scale magnetic fields in astrophysics. It is shown that, in magnetohydrodynamic turbulence, unst...

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Bibliographic Details
Published in:Physics of plasmas 2022-07, Vol.29 (7)
Main Authors: Tripathi, B., Fraser, A. E., Terry, P. W., Zweibel, E. G., Pueschel, M. J.
Format: Article
Language:English
Subjects:
Astrophysics
Dynamic stability
Energy transfer
Fluid dynamics
Fluid flow
Magnetic fields
Magnetic variations
Magnetohydrodynamic turbulence
Magnetohydrodynamics
Sequestering
Shear flow
Stability analysis
Turbulent flow
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Summary:Straining of magnetic fields by large-scale shear flow, which is generally assumed to lead to intensification and generation of small scales, is reexamined in light of the persistent observation of large-scale magnetic fields in astrophysics. It is shown that, in magnetohydrodynamic turbulence, unstable shear flows have the unexpected effect of sequestering magnetic energy at large scales due to counteracting straining motion of nonlinearly excited large-scale stable eigenmodes. This effect is quantified via dissipation rates, energy transfer rates, and visualizations of magnetic field evolution by artificially removing the stable modes. These analyses show that predictions based upon physics of the linear instability alone miss substantial dynamics, including those of magnetic fluctuations.
ISSN:1070-664X
1089-7674
DOI:10.1063/5.0096886