CATASTROPHIC QUENCHING IN alpha Omega DYNAMOS REVISITED
2012 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 748, no 1, 51- p.Article in journal (Refereed) Published
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(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.
Place, publisher, year, edition, pages
2012. Vol. 748, no 1, 51- p.
magnetic fields, magnetohydrodynamics (MHD), turbulence
Astronomy, Astrophysics and Cosmology
IdentifiersURN: urn:nbn:se:su:diva-76119DOI: 10.1088/0004-637X/748/1/51ISI: 000301347500051OAI: oai:DiVA.org:su-76119DiVA: diva2:526197