CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED
Journal Article
·
· Astrophysical Journal
- NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE 10691 Stockholm (Sweden)
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.
- OSTI ID:
- 22016164
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 748; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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