Coherent mode detected by ECEI in pedestal region on EAST tokamak

A coherent mode is detected by electron cyclotron emission imaging (ECEI) diagnostic in the pedestal region during ELM-free phase and inter-ELM phase on the Experimental Advanced Super-conducting Tokamak (EAST). In the normal high confinement regime (H-mode) with co-current neutral beam injection (NBI), the coherent mode grows a few milliseconds after L-H transition, and the mode frequency downshifts from about 45 kHz to 15 kHz lasting for about 100 ms before the first ELM crash. It is obvious to say that the mode rotates in the electron diamagnetic direction in the laboratory frame through ECE imaging. Ballooning-like mode structure is identified. The estimated poloidal mode number is m > 25, and toroidal mode number is n > 5 for the local safety factor q ∼ 5. Wave length of the mode increases until the mode saturates, which is consistent with the result that the estimated poloidal mode number decreases. Characteristics of the mode during inter-ELM phase are similar to that during ELM free phase. (author)