Suppression of molybdenum impurity accumulation in the core using on-axis electron cyclotron resonance heating in EAST

Core metal impurity transport in an electron cyclotron resonance heating (ECRH) plasma is investigated for the first time in experimental advanced superconducting tokamak, on the basis of profile measurements of impurity emissions using space-resolved extreme ultraviolet spectroscopy. A significant reduction in the core molybdenum emissivity is observed during the on-axis ECRH phase, accompanied by decreased core electron density and increased electron temperature. The impurity transport study before and during ECRH injection is performed using line emissions of Mo XXIX, Mo XXX, Mo XXXI, and Mo XXXII with the core impurity transport code, STRAHL. It is found that the diffusion coefficient increases substantially and that the value of the diffusion coefficient is about one order of magnitude higher than that of neoclassical transport. Also, the inward convective velocity decreases and even changes its direction in the core region (q < 0.5) during on-axis ECRH, which is thought to dominantly contribute to the reduction in core impurity ion density.