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Title: CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED

Abstract

At large magnetic Reynolds numbers, magnetic helicity evolution plays an important role in astrophysical large-scale dynamos. The recognition of this fact led to the development of the dynamical {alpha} quenching formalism, which predicts catastrophically low mean fields in open systems. Here, we show that in oscillatory {alpha}{Omega} dynamos this formalism predicts an unphysical magnetic helicity transfer between scales. An alternative technique is proposed where this artifact is removed by using the evolution equation for the magnetic helicity of the total field in the shearing advective gauge. In the traditional dynamical {alpha} quenching formalism, this can be described by an additional magnetic helicity flux of small-scale fields that does not appear in homogeneous {alpha}{sup 2} dynamos. In {alpha}{Omega} dynamos, the alternative formalism is shown to lead to larger saturation fields than what has been obtained in some earlier models with the traditional formalism. We have compared the predictions of the two formalisms to results of direct numerical simulations, finding that the alternative formulation provides a better fit. This suggests that worries about catastrophic dynamo behavior in the limit of large magnetic Reynolds number are unfounded.

Authors:
;  [1]
  1. NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE 10691 Stockholm (Sweden)
Publication Date:
OSTI Identifier:
22016164
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 748; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; COMPUTERIZED SIMULATION; COSMOLOGICAL MODELS; COSMOLOGY; EQUATIONS; GALACTIC EVOLUTION; HELICITY; MAGNETIC FIELDS; MAGNETIC REYNOLDS NUMBER; MAGNETOHYDRODYNAMICS; MEAN-FIELD THEORY

Citation Formats

Hubbard, Alexander, and Brandenburg, Axel, E-mail: alex.i.hubbard@gmail.com. CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED. United States: N. p., 2012. Web. doi:10.1088/0004-637X/748/1/51.
Hubbard, Alexander, & Brandenburg, Axel, E-mail: alex.i.hubbard@gmail.com. CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED. United States. doi:10.1088/0004-637X/748/1/51.
Hubbard, Alexander, and Brandenburg, Axel, E-mail: alex.i.hubbard@gmail.com. 2012. "CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED". United States. doi:10.1088/0004-637X/748/1/51.
@article{osti_22016164,
title = {CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED},
author = {Hubbard, Alexander and Brandenburg, Axel, E-mail: alex.i.hubbard@gmail.com},
abstractNote = {At large magnetic Reynolds numbers, magnetic helicity evolution plays an important role in astrophysical large-scale dynamos. The recognition of this fact led to the development of the dynamical {alpha} quenching formalism, which predicts catastrophically low mean fields in open systems. Here, we show that in oscillatory {alpha}{Omega} dynamos this formalism predicts an unphysical magnetic helicity transfer between scales. An alternative technique is proposed where this artifact is removed by using the evolution equation for the magnetic helicity of the total field in the shearing advective gauge. In the traditional dynamical {alpha} quenching formalism, this can be described by an additional magnetic helicity flux of small-scale fields that does not appear in homogeneous {alpha}{sup 2} dynamos. In {alpha}{Omega} dynamos, the alternative formalism is shown to lead to larger saturation fields than what has been obtained in some earlier models with the traditional formalism. We have compared the predictions of the two formalisms to results of direct numerical simulations, finding that the alternative formulation provides a better fit. This suggests that worries about catastrophic dynamo behavior in the limit of large magnetic Reynolds number are unfounded.},
doi = {10.1088/0004-637X/748/1/51},
journal = {Astrophysical Journal},
number = 1,
volume = 748,
place = {United States},
year = 2012,
month = 3
}
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