Collapse events at the q = 2 surface occurring during the mode locking process of an m/n = 2/1 tearing mode have been observed on TEXTOR. The plasma confinement within the q = 2 surface collapses without much influence on the width of the island (O-point). With an external rotating resonant magnetic perturbation (RMP) field induced by the dynamic ergodic divertor, secondary structures moving near the separatrix of the primary large 2/1 island with the same frequency as the RMP have been observed after the collapse events. The plasma confinement recovers when the secondary structures vanish.
Theoretical model of the plasma edge. II. Transport along the open field lines of a magnetic island belt associated with the ionization instability