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Nonhelical Inverse Transfer of a Decaying Turbulent Magnetic Field
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.ORCID iD: 0000-0002-7304-021X
2015 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 7, 075001Article in journal (Refereed) Published
Abstract [en]

In the presence of magnetic helicity, inverse transfer from small to large scales is well known in magnetohydrodynamic (MHD) turbulence and has applications in astrophysics, cosmology, and fusion plasmas. Using high resolution direct numerical simulations of magnetically dominated self-similarly decaying MHD turbulence, we report a similar inverse transfer even in the absence of magnetic helicity. We compute for the first time spectral energy transfer rates to show that this inverse transfer is about half as strong as with helicity, but in both cases the magnetic gain at large scales results from velocity at similar scales interacting with smaller-scale magnetic fields. This suggests that both inverse transfers are a consequence of universal mechanisms for magnetically dominated turbulence. Possible explanations include inverse cascading of the mean squared vector potential associated with local near two dimensionality and the shallower k(2) subinertial range spectrum of kinetic energy forcing the magnetic field with a k(4) subinertial range to attain larger-scale coherence. The inertial range shows a clear k(-2) spectrum and is the first example of fully isotropic magnetically dominated MHD turbulence exhibiting weak turbulence scaling.

Place, publisher, year, edition, pages
2015. Vol. 114, no 7, 075001
Keyword [en]
Astrophysics, Energy transfer, Kinetic energy, Kinetics, Magnetic fields, Magnetism, Magnetohydrodynamics, Turbulence, Inertial ranges, Inverse transfer, Magnetic helicity, Spectral energy transfer, Turbulent magnetic fields, Two dimensionality, Universal mechanisms, Vector potential
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-163475DOI: 10.1103/PhysRevLett.114.075001ISI: 000350274900007PubMedID: 25763960ScopusID: 2-s2.0-84923313255OAI: diva2:800669
Swedish Research Council, 621-2011-5076 2012-5797EU, European Research Council, 227952

QC 20150407

Available from: 2015-04-07 Created: 2015-04-07 Last updated: 2015-04-07Bibliographically approved

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Brandenburg, Axel
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