What will ITER do about the large islands that trigger disruptions?

Experience with disruptions in JET suggests that many of the disruptions in ITER will be preceded by the growth of large islands. 95% of the disruptions in JET have been preceded by locked modes [1]. Analysis of disruption data on JET has found that islands grew to 30% of the minor radius before a disruption was triggered [2]. The islands grow on a resistive time scale. It will be desirable to deal with these islands before they trigger a mitigation event. However, the ECCD island stabilization capability on ITER has been optimized for the stabilization of small islands produced by neoclassical tearing modes. With the toroidal launch angle of the upper launchers fixed at 20 degrees, they are not well suited for the stabilization of large islands produced by other off-normal events. It will be desirable to make the mirrors of the upper launchers steerable in the toroidal angle. This will be particularly useful for increasing the current drive efficiency when the q=2 surface shifts inward. Nonlinear effects will be significant [3]. They can be used to advantage but must in any case be accounted for in aiming the EC to avoid degradation of the stabilization capability.