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A coherent mode (CM) in the edge pedestal region has been observed on different fluctuation quantities, including density fluctuation, electron temperature fluctuation and magnetic fluctuation in H mode plasma on the Experimental Advanced Superconducting Tokamak (EAST) tokamak. Measurements at different poloidal positions show that the local poloidal wavenumber is smallest at the outboard midplane and will increase with poloidal angle. This poloidal asymmetry is consistent with the flute-like assumption (i.e. k // ∼0) from which the toroidal mode number of the mode has been estimated as between 12 and 17. It was further found that the density fluctuation amplitude of the CM also demonstrated poloidal asymmetry. The appearance of a CM can clearly decrease or even stop the increase in the edge density, while the disappearance of a CM will lead to an increase in the pedestal density and density gradient. Statistical analysis showed there was a trend that as the CM mode amplitude increased, the rate of increase of the edge density decreased and the particle flux (Γ div ) onto the divertor plate increased. The CM sometimes showed burst behavior, and these bursts led bursts on Γ div with a time of about 230 μs, which is close to the time for particle flow from the outer midplane to the divertor targets along the scrape-off layer magnetic field line. This evidence showed that the CM had an effect on the outward transport of particles.

Turbulence in the pedestal region of the EAST tokamak has been observed and studied using reflectometry. In lower hybrid wave (LHW) or neutral beam injection (NBI) dominated heating plasma, a coherent mode (CM) was usually observed in the ELM-free phase just after the L-H transition. The CM rotated in the electron diamagnetic drift (EDD) direction in the laboratory frame with a poloidal wave number (k θ ) of 0.5 cm −1 -0.7 cm −1 and its frequency usually chirped from 80 -100 kHz down to 40 -50 kHz as the pedestal evolved. The appearance of this mode reduced the increasing rate of pedestal pressure, implying that the CM may have an effect on outward pedestal transport. This mode can exist every ten milliseconds and is finally replaced by broadband (BB) fluctuation in the later ELM-free phase. It was found that the appearance and disappearance of the CM was correlated to the pedestal pressure. In the inter-ELM phase, the pedestal turbulence is generally dominated by BB fluctuation with poloidal wave numbers from 0 to 3 cm −1 rotating in the EDD direction in the laboratory frame. Analysis shows that the pedestal pressure increasing rate dp e, ped /dt decreases with the amplitude of the BB fluctuation, implying that the BB fluctuation may play an important role in pedestal evolution. The preliminary observation on the fluctuation just inside the pedestal top is also presented.