NTM Suppression and Avoidance at DIII-D Using Real-Time Mirror Steering

The Electron Cyclotron Current Drive (ECCD) real-time steerable mirrors at DIII-D were developed and successfully operated to avoid and suppress neoclassical tearing modes (NTM). The NTM avoidance/suppression control logic moves the deposition location of the ECCD with six sets of real-time steerable mirrors in order to align it with the NTM location. The steerable mirrors enable changing the deposition location at approximately 2 m/s with accuracy of a few millimeters while keeping the plasma radial position and the toroidal field constant during NTM avoidance/suppression. The real-time system enables simultaneous avoidance/suppression of multiple magnetic islands (such as $m/n=2/1$ and 3/2 islands).