Toward the universality of low-n RMP-driven, ELM-crash-suppression physics

The onset of resonant magnetic perturbation (RMP)-driven, ELM-crash-suppression still lacks in the universal physics understanding. To address the commonalities and discrepancies among tokamaks, a series of inter-machine comparison experiments of RMP are in progress. A recent similarity experiment done in DIII-D using KSTAR-similar shape (KSS) plasma (with the triangularity of δ ~0.6) demonstrated a merit of highly shaped plasmas, which turned out to be quite resilient against mode-locking during n=1 RMP. Specifically, even up to the maximum available n=1 RMP currents in both in-vessel and ex-vessel coils, the discharge with KSS survived without detrimental mode-lockings, which allowed a systematic phasing scan of n=1 RMP in DIII-D. Despite the a-priori knowledge about effective modeling-based 3-D configuration for ELM-crash-suppression, the attempts of n=1 RMP in DIII-D have not led to full suppression of ELM-crashes yet. Currently, we speculate that non-optimal edge/divertor recycling might have been influenced by the inadequate divertor pumping position associated with the unusual high value of triangularity.