Experimental study of long-lived saturated mode in EAST ELM-free H mode sawtoothing plasma

Two types of long-lived saturated impurity ions induced modes (LLMs) including ideal-like kink mode which damp before large sawtooth crash, termed sawtooth-free LLMs (SF-LLMs) and complex LLMs (C-LLMs, similar with LLMs reported in C-Mod) which coexistence with compound sawtooth and final damping by sawtooth crash were observed in EAST ELM-free H mode sawtoothing plasma. The strong coupling of C-LLMs and 2/1 tearing mode (TM) can trigger neo-classic tearing mode (NTM) after sawtooth crash. The frequencies of LLMs are related to the plasma toroidal rotation. Finally, discussion about the role of lower hybrid current drive (LHCD) driven current to large compound sawtooth and the role of fast particles produced by LHCD to the excitation of LLMs were also given in this paper. (author)