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Varying the forcing scale in low Prandtl number dynamos
Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy. University of Colorado, USA.
Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Meteorology . University of Colorado, USA.
Number of Authors: 42018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 479, no 2, p. 2827-2833Article in journal (Refereed) Published
Abstract [en]

Small-scale dynamos are expected to operate in all astrophysical fluids that are turbulent and electrically conducting, for example the interstellar medium, stellar interiors, and accretion discs, where theymay also be affected by or competing with large-scale dynamos. However, the possibility of small-scale dynamos being excited at small and intermediate ratios of viscosity to magnetic diffusivity (the magnetic Prandtl number) has been debated, and the possibility of them depending on the large-scale forcing wavenumber has been raised. Here, we show, using four values of the forcing wavenumber, that the small-scale dynamo does not depend on the scale separation between the size of the simulation domain and the integral scale of the turbulence, i.e. the forcing scale. Moreover, the spectral bottleneck in turbulence, which has been implied as being responsible for raising the excitation conditions of small-scale dynamos, is found to be invariant under changing the forcing wavenumber. However, when forcing at the lowest few wavenumbers, the effective forcing wavenumber that enters in the definition of the magnetic Reynolds number is found to be about twice the minimum wavenumber of the domain. Our work is relevant to future studies of small-scale dynamos, of which several applications are being discussed.

Place, publisher, year, edition, pages
2018. Vol. 479, no 2, p. 2827-2833
Keywords [en]
dynamo, magnetic fields, MHD, turbulence, Sun: dynamo
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-160049DOI: 10.1093/mnras/sty1570ISI: 000441380100096OAI: oai:DiVA.org:su-160049DiVA, id: diva2:1255309
Available from: 2018-10-11 Created: 2018-10-11 Last updated: 2018-10-11Bibliographically approved

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Brandenburg, AxelLi, Xiang-Yu
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