Stabilization of Neoclassical Tearing Modes in Tokamaks by Radio Frequency Current Drive

Resistive neoclassical tearing modes (NTMs) will be the principal limit on stability and performance in the ITER standard scenario as the resulting islands break up the magnetic surfaces that confine the plasma. Drag from rotating island‐induced eddy current in the resistive wall can also slow the plasma rotation, produce locking to the wall, and cause loss of high confinement H‐mode and disruption. The NTMs are maintained by helical perturbations to the pressure‐gradient driven “bootstrap” current. Thus, this is a high beta instability even at the modest beta for ITER. A major line of research on NTM stabilization is the use of radio frequency (rf) current drive at the island rational surface. While large, broad current drive from lower hybrid waves has been shown to be stabilizing (COMPASS‐D), most research is directed to small, narrow current drive from electron cyclotron waves (ECCD); ECCD stabilization and/or preemptive prevention is successful in ASDEX Upgrade, DIII‐D and JT‐60U, for example, with a...