The investigation of quasi coherent mode on EAST using Doppler reflectometry

An electrostatic Quasi coherent mode has been observed in density fluctuations and perpendicular velocity fluctuations with the frequency range of 3–80 kHz on the Experimental Advanced Superconducting Tokamak using multi-channel Doppler reflectometry. It appears in the edge localized mode (ELM)-free period after L-H transition or in the inter-ELM period. The mode rotates almost together with the plasma with the poloidal wave number around 0.6 and its frequency chirps with plasma poloidal velocity. The mode can exist in a large radial coverage (ρ = 0.75–0.98), and peaks near the top of pedestal, suggesting that it might be excited in the steep gradient pedestal region, and spread into the core area.