Journal Article

Magnetorotational instability driven dynamos at low magnetic Prandtl numbers

P. J. Käpylä and M. J. Korpi

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 413, issue 2, pages 901-907
Published in print May 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI:
Magnetorotational instability driven dynamos at low magnetic Prandtl numbers

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Numerical simulations of the magnetorotational instability (MRI) with zero initial net flux in a non-stratified isothermal cubic domain are used to demonstrate the importance of magnetic boundary conditions. In fully periodic systems, the level of turbulence generated by the MRI strongly decreases as the magnetic Prandtl number (Pm), which is the ratio of kinematic viscosity and magnetic diffusion, is decreased. No MRI or dynamo action below Pm = 1 is found, agreeing with earlier investigations. Using vertical field conditions, which allow the generation of a net toroidal flux and magnetic helicity fluxes out of the system, the MRI is found to be excited in the range 0.1 ≤ Pm ≤ 10, and the saturation level is independent of Pm. In the vertical field runs, strong mean-field dynamo develops and helps to sustain the MRI.

Keywords: accretion, accretion discs; magnetic fields; MHD; turbulence

Journal Article.  4921 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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