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Author Bodo, G. ♦ Rossi, P. ♦ Cattaneo, F. ♦ Mignone, A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ ACCRETION DISKS ♦ APPROXIMATIONS ♦ BOUNDARY CONDITIONS ♦ GAUGE INVARIANCE ♦ HELICITY ♦ MAGNETIC FLUX ♦ MAGNETOHYDRODYNAMICS ♦ SPACE ♦ SYMMETRY ♦ TURBULENCE
Abstract We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by magneto-rotational turbulence (MRT) within the shearing-box approximation. 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 the average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and the helicity flux for several realizations of dynamo action. We find in these cases that the system as a whole does not break reflectional symmetry and that 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 and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-07-10
Publisher Place United States
Journal Astrophysical Journal
Volume Number 843
Issue Number 2


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