Observation of plasma performance Improvement by edge ECRH power deposition on Experimental Advanced Superconducting Tokamak

Edge electron cyclotron current drive (ECCD) has been observed to enhance plasma performance on the Experimental Advanced Superconducting Tokamak (EAST). By adjusting the ECCD mirror, the power deposition was shifted from the core to the edge region during H-mode operation. This edge ECCD deposition resulted in a reduction of plasma density and tungsten impurity, while simultaneously steepening the electron and ion temperature profiles, thereby improving overall confinement. Correspondingly, the core safety factor increased, leading to the formation of a negative magnetic shear in the core, which is attributed to suppressing the ion temperature gradient (ITG) turbulence, as confirmed by poloidal correlation reflectometry (PCR) diagnostics. Theoretical simulations indicate the coexistence of density gradient-driven trapped electron mode (TEM) turbulence in the core (ρ_t<0.45) and ITG turbulence at the edge (ρ_t>0.45). Suppression of these turbulences contribute to the enhancement of plasma confinement, which results in a significant reduction of the inward convective velocity of tungsten.