Confined disruption of a three-dimensional twisted magnetic flux tube

In this Letter, we study the evolution of a magnetic flux tube confined by an overlaying arcade, considering the gradual build up of the twist in the flux tube. During a first stage, the magnetic field evolves quasi-statically through a sequence of force-free equilibria, building up self-helicity (twist) in the flux rope. When a sufficient amount of twist is injected in the system, it cannot reach a neighboring equilibrium and experiences a major disruption in which the magnetic field of the flux tube reconnects with the overlaying arcade. After the relaxation is completed, the configuration remains globally closed and consists of two almost untwisted flux tubes and a closed overlaying arcade. The model might represent a basis for a unified theory of noneruptive and eruptive flares, in which twisted magnetic flux tubes play a crucial role.