Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Abstract

ABSTRACT Magnetic flux tubes such as those in the solar corona are subject to a number of instabilities. Important among them is the kink instability that plays a central part in the nanoflare theory of coronal heating, and for this reason in numerical simulations, it is usually induced by tightly controlled perturbations and studied in isolation. In contrast, we find that fluting modes of instability are readily excited when disturbances are introduced in our magnetohydrodynamic flux tube simulations by dynamic twisting of the flow at the boundaries. We also find that the flute instability, which has been theorized but rarely observed in the coronal context, is strongly enhanced when plasma viscosity is assumed anisotropic. We proceed to investigate the co-existence and competition between flute and kink instabilities for a range of values of the resistivity and of the parameters of the anisotropic and isotropic models of viscosity. We conclude that while the flute instability cannot prevent the kink from ultimately dominating, it can significantly delay its development especially at strong viscous anisotropy induced by intense magnetic fields.