ELM control experiments in the KSTAR device

Abstract

The fourth KSTAR campaign in 2011 concentrated on active edge-localized mode (ELM) control by various methods such as non-axisymmetric magnetic perturbations, supersonic molecular beam injection (SMBI), vertical jogs of the plasma column and edge electron heating. The segmented in-vessel control coil (IVCC) system is capable of applying n <= 2 perturbed field with different phasing among top, middle and bottom coils. Application of an n = 1 perturbed field showed a desirable ELM suppression result. Fast vertical jogs of the plasma column achieved ELM pace-making and ELMs locked to 50 Hz vertical jogs were observed with a high probability of phase locking. A newly installed SMBI system was used for ELM control and the state of mitigated ELMs was sustained by the optimized repetitive SMBI pulse for a few tens of ELM periods. A change in ELM behaviour was seen due to edge electron heating although the effect of ECH launch needs supplementary analyses. The ECEI images of suppressed/mitigated ELM states showed apparent differences when compared with natural ELMy states. Further analyses are ongoing to explain the observed ELM control results.