Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence
Journal
Date Issued
2017
Author(s)
Abstract
We examine the relationship between magnetic flux generation and magnetic
helicity in a simple model of dynamo action. We consider dynamo action driven
by Magneto-Rotational Turbulence (MRT) within the shearing-box approxima-
tion. We consider magnetically open boundary conditions that allow a flux of
helicity in or out of the computational domain. We circumvent the problem of
the lack of gauge invariance in open domains by choosing a particular gauge –
the winding gauge – that provides a natural interpretation in terms of average
winding number of pairwise field lines. We use this gauge precisely to define and
measure the helicity and helicity flux for several realizations of dynamo action.
We find that the system as a whole does not break reflectional symmetry and
the total helicity remains small even in cases when substantial magnetic flux is
generated. We find no particular connection between the generation of magnetic
flux – large-scale dynamo action – and the helicity or the helicity flux though
the volume. We suggest that this result may be due to the essentially nonlinear
nature of the dynamo processes in MRT.
Volume
843
Issue
2
Start page
86
Issn Identifier
0004-637X
Ads BibCode
2017ApJ...843...86B
Rights
open.access
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