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Quantifying the effect of turbulent magnetic diffusion on the growth rate of the magneto-rotational instability
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.ORCID-id: 0000-0002-7304-021X
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2014 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 567, artikel-id A139Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context. In astrophysics, turbulent diffusion is often used in place of microphysical diffusion to avoid resolving the small scales. However, we expect this approach to break down when time and length scales of the turbulence become comparable with other relevant time and length scales in the system. Turbulent diffusion has previously been applied to the magneto-rotational instability (MRI), but no quantitative comparison of growth rates at different turbulent intensities has been performed. Aims. We investigate to what extent turbulent diffusion can be used to model the effects of small-scale turbulence on the kinematic growth rates of the MRI, and how this depends on angular velocity and magnetic field strength. Methods. We use direct numerical simulations in three-dimensional shearing boxes with periodic boundary conditions in the spanwise direction and additional random plane-wave volume forcing to drive a turbulent flow at a given length scale. We estimate the turbulent diffusivity using a mixing length formula and compare with results obtained with the test-field method. Results. It turns out that the concept of turbulent diffusion is remarkably accurate in describing the effect of turbulence on the growth rate of the MRI. No noticeable breakdown of turbulent diffusion has been found, even when time and length scales of the turbulence become comparable with those imposed by the MRI itself. On the other hand, quenching of turbulent magnetic diffusivity by the magnetic field is found to be absent. Conclusions. Turbulence reduces the growth rate of the MRI in the same way as microphysical magnetic diffusion does.

Ort, förlag, år, upplaga, sidor
2014. Vol. 567, artikel-id A139
Nyckelord [en]
turbulence, magnetohydrodynamics (MHD), hydrodynamics
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
URN: urn:nbn:se:su:diva-108218DOI: 10.1051/0004-6361/201322837ISI: 000341185300030OAI: oai:DiVA.org:su-108218DiVA, id: diva2:755866
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AuthorCount:5;

Tillgänglig från: 2014-10-15 Skapad: 2014-10-15 Senast uppdaterad: 2019-12-12Bibliografiskt granskad

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Brandenburg, Axel
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Nordiska institutet för teoretisk fysik (Nordita)Institutionen för astronomi
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Astronomy and Astrophysics
Astronomi, astrofysik och kosmologi

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