This work presents an investigation conducted on the Experimental Advanced Superconducting Tokamak high-density H-mode discharges with low-Z impurity (argon) injection, aiming to explore potential approaches and mechanisms for the recovery of core energy confinement. A clear increase in H98 and Ti was observed following impurity injection, accompanied by a simultaneous decrease in density. The quasi-linear Trapped Gyro-Landau Fluid model is employed for analysis. Modeling results show that core low-k ion temperature gradient (ITG) modes are stabilized, which corresponds to the observed reduction in ion heat flux. It is mainly attributed to the dilution of main ions, which raises the ITG instability threshold. Moreover, the increase in during this process further elevates the ITG threshold, creating a positive feedback effect. Impurity injection also leads to an increase in the collisionality, which enhances the outward pure convective pinch of particle flux in the outer region, thereby triggering a reduction in electron density. Additionally, TGYRO simulation results unambiguously eliminate weakly enhanced toroidal rotation as the causal mechanism for the observed confinement improvement. Instead, the simulations indicate that a deeply deposited fueling source can both compensate for density reduction and enhance density peaking.
This paper investigates the recovery of core energy confinement and density reduction in EAST high-density H-mode plasmas following low-Z impurity (argon) injection. The results show that impurity injection stabilizes core ion temperature gradient (ITG) modes, leading to improved energy confinement and reduced density. This is attributed to main ion dilution and increased collisionality, which enhances outward particle transport. The findings provide insights into potential approaches for confinement improvement in high-density fusion plasmas.