On the MHD stability of the = 1 kink mode in solar coronal loops

Observatoire Astronomique, 11 rue de l'Université, 67000 Strasbourg, France

Corresponding author: H. Baty, baty@astro.u-strasbg.fr

Received: 4 September 2000
Accepted: 15 November 2000

Abstract

We revisit the ideal MHD stability of the kink mode in configurations representative of coronal loops, using a stability code. We adopt different magnetic force-free equilibria defined by the twist function that are embedded into an outer potential field situated at a radial distance r₀ from the magnetic axis. In the limit , l₀ being the axis pitch length, the configurations are driven unstable by the kink mode when the twist exceeds the classical critical value of on the axis. However, the critical axis twist strongly depends on the equilibrium in the opposite limit, with sharply increasing values when r₀ becomes of the order or smaller than l₀. We interpret these results in terms of the stability criterion , where is the twist value averaged over a radial length l. It is found that l is of the order of 3-4 times l₀, provided ; otherwise it depends on the twist profile via the existence of magnetic resonances.