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

Naturally occurring error elds in tokamaks, which arise from misalignments of the external eld coils, may trigger the onset of tearing modes. The conditions under which a static error eld is able to lock a rotating tearing mode and how this process takes place are discussed. The analysis presented 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.