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Magnetic Prandtl number dependence of the kinetic-to-magnetic dissipation ratio
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.ORCID iD: 0000-0002-7304-021X
2014 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 791, no 1, 12Article in journal (Refereed) Published
Abstract [en]

Using direct numerical simulations of three-dimensional hydromagnetic turbulence, either with helical or non-helical forcing, we show that the kinetic-to-magnetic energy dissipation ratio always increases with the magnetic Prandtl number, i.e., the ratio of kinematic viscosity to magnetic diffusivity. This dependence can always be approximated by a power law, but the exponent is not the same in all cases. For non-helical turbulence, the exponent is around 1/3, while for helical turbulence it is between 0.6 and 2/3. In the statistically steady state, the rate of energy conversion from kinetic into magnetic by the dynamo must be equal to the Joule dissipation rate. We emphasize that for both small-scale and large-scale dynamos, the efficiency of the energy conversion depends sensitively on the magnetic Prandtl number, and thus on the microphysical dissipation process. To understand this behavior, we also study shell models of turbulence and one-dimensional passive and active scalar models. We conclude that the magnetic Prandtl number dependence is qualitatively best reproduced in the one-dimensional model as a result of dissipation via localized Alfvén kinks.

Place, publisher, year, edition, pages
2014. Vol. 791, no 1, 12
Keyword [en]
accretion, accretion disks, hydrodynamics, magnetohydrodynamics (MHD), shock waves, turbulence
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-161765DOI: 10.1088/0004-637X/791/1/12ISI: 000339657700012ScopusID: 2-s2.0-84905169951OAI: diva2:799442
EU, European Research Council, 227952Swedish Research Council, 621-2011-5076 2012-5797

QC 20150331

Available from: 2015-03-31 Created: 2015-03-17 Last updated: 2015-03-31Bibliographically approved

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