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Title: Magnetic Helicities and Dynamo Action in Magneto-rotational 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.

Authors:
;  [1];  [2];  [3]
  1. INAF/Osservatorio Astrofisico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese (Italy)
  2. Department of Astronomy and Astrophysics, The University of Chicago, 5640 S. Ellis Avenue, Chicago IL 60637 (United States)
  3. Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino (Italy)
Publication Date:
OSTI Identifier:
22663424
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 843; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; APPROXIMATIONS; BOUNDARY CONDITIONS; GAUGE INVARIANCE; HELICITY; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; SPACE; SYMMETRY; TURBULENCE

Citation Formats

Bodo, G., Rossi, P., Cattaneo, F., and Mignone, A., E-mail: bodo@oato.inaf.it. Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA7680.
Bodo, G., Rossi, P., Cattaneo, F., & Mignone, A., E-mail: bodo@oato.inaf.it. Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence. United States. doi:10.3847/1538-4357/AA7680.
Bodo, G., Rossi, P., Cattaneo, F., and Mignone, A., E-mail: bodo@oato.inaf.it. Mon . "Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence". United States. doi:10.3847/1538-4357/AA7680.
@article{osti_22663424,
title = {Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence},
author = {Bodo, G. and Rossi, P. and Cattaneo, F. and Mignone, A., E-mail: bodo@oato.inaf.it},
abstractNote = {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.},
doi = {10.3847/1538-4357/AA7680},
journal = {Astrophysical Journal},
number = 2,
volume = 843,
place = {United States},
year = {Mon Jul 10 00:00:00 EDT 2017},
month = {Mon Jul 10 00:00:00 EDT 2017}
}