Mode entrainment to study effect of islands on ECCD at DIII-D

An experiment was performed on the efficiency of ECCD in affecting 2/1 tearing mode amplitude in slowly rotating plasmas. The slow rotation was accomplished by rotating magnetic perturbations applied by the I-coil, and entrainment at 70 Hz was very successful, taking place on most shots. The effect of ECCD was hard to see in most cases because the rotating mode, similar to a locked mode, caused the plasma temperature to be rather low, so that the current driven by the ECCD was small. Attempts to move the q=2 surface closer to the axis to improve the ECCD were unsuccessful. In several cases it appears that the ECCD did shrink the island until it unlocked and the H-mode was restored. 

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