Identification of an edge coherent mode in an EAST electron cyclotron resonance heated H-mode plasma

In a purely electron cyclotron resonance heated plasma at the EAST tokamak, an electrostatic edge coherent mode (ECM) is observed to emerge after the L-H transition and disappear following the first large edge localized mode burst, exhibiting an initial frequency of 80 kHz that subsequently decreases to 20–30 kHz in stationary phase. Using multiple internal fluctuation diagnostics, the ECM is shown to be localized in the pedestal region, with a poloidal wavenumber of k θ =0.6–0.7 cm -1 and an estimated toroidal mode number of n=12–15. Linear gyrokinetic simulations with the CGYRO code suggest the ECM to be a dissipative trapped electron mode, driven by the electron pressure gradient and high collisionality.