An innovative interpretation of rotating tearing mode locking to an external static current

Naturally occurring error fields in tokamaks, which arise from misalignment s of the external field coils, may trigger the onset of tearing modes. The conditions under which a static error field is able to lock a rotating tear ing mode and how this process takes place are discussed. The analysis prese nted contributes to a new understanding and interpretation of mode locking, given in terms of the superposition of a slipping layer (a radial layer of very fast mode phase variations) and the tearing layer, where reconnection takes place. In addition, a stabilizing operating window is found to exist , independent of the phase time evolution of the mode.