Astronomy & Astrophysics

A&A 477, 35-41 (2008)
DOI: 10.1051/0004-6361:20077476

Stability of magnetic configurations containing the toroidal and axial fields

A. Bonanno^{1, 2} and V. Urpin^{1, 3}

¹ INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
e-mail: abo@oact.inaf.it
² INFN, Sezione di Catania, via S. Sofia 72, 95123 Catania, Italy
³ A.F. Ioffe Institute of Physics and Technology and Isaac Newton Institute of Chile, Branch in St. Petersburg, 194021 St. Petersburg, Russia

(Received 14 March 2007 / Accepted 18 September 2007)

Abstract
Stability properties of magnetic-field configurations containing the toroidal and axial field are considered. The stability is treated by making use of linear analysis. It is shown that the conditions required for the onset of instability are essentially different from those given by the necessary condition ${\rm d} (s B_{\varphi})/{\rm d}s > 0$ , where s is the cylindrical radius. The growth rate of instability is calculated for a wide range of the parameters. We argue that the instability can operate in two different regimes depending on the strength of the axial field and the profile of the toroidal field.

Key words: magnetohydrodynamics (MHD) -- instabilities -- stars: magnetic fields