Experimental and modeling study of the impact of upstream D2 puff on divertor detachment and impurity control with argon seeding in EAST.

Radiative divertor is an effective method for the divertor heat flux control, but excessive core impurity radiation can deteriorate the confinement in tokamaks. In recent EAST experiments, the compatibility of divertor detachment and impurity control with good core confinement (H_98,y2 ∼1) has been achieved simultaneously by combining an upstream deuterium (D₂) puff and divertor argon (Ar) seeding. Both experimental and SOLPS-ITER modeling reveal that additional D₂ puff can further mitigate the target heat load and facilitate the detachment. The SOLPS-ITER results also show that the D₂ puff makes a limited contribution to the Ar line radiation but a significant contribution to the neutral radiation in the SOL and divertor regions. The physical mechanism behind the effect of the D₂ puff on the Ar retention is also revealed by the modeling. The increase in the Ar velocity is the major reason for the improved Ar retention in the partial detachment state. The increase in v_Ar is mainly caused by the strengthening of frictional drag of D⁺, which is because the additional D₂ puff increases the pressure gradient force (FPG) and the electric field force (FE) on D⁺. Further analysis reveals that in the deep detachment state, some other negative effects play a dominant role in determining the Ar retention, such as the shift of the region of the Ar⁺ ionization source, the decrease in the strength of the Ar⁺ ionization source, and the net force on the Ar ions near the target. [ABSTRACT FROM AUTHOR]