Eruption of a helically twisted prominence

In this paper we analyze the eruption of a prominence, characterized by a helical-like structure and by a non-linear rising motion. We approximated the prominence as a cylindrical curved flux tube and estimated the behaviour of several geometrical parameters during the activation and the eruption phases. We determined that, at the onset of the activation, the number N of turns of a mag- netic field line over the whole length of the prominence was ∼ 5.0, while the value of the ratio P /r0 between the pitch of the magnetic field lines and the prominence width was ∼ 0.45. These values are in good agreement with those predicted by the kink-mode instability. Moreover, we found a decrease of the total twist of one helical thread from ∼ 10π to ∼ 2π during the prominence eruption, indicating a relaxation of the magnetic field towards a less twisted configuration. We conclude that the prominence was initially destabilized by the kink-mode instability and, not succeeding in finding a new equilibrium configuration, it erupted.