Correlation between impurity radiation rollover and divertor detachment with boundary impurity seeding in HL-2A

Divertor detachment has significant potential for reducing the divertor target thermal load, and impurity seeding is the primary method for achieving divertor detachment. In this study, different impurity seeding scenarios (N, Ne, and Ar) at the boundary region of HL-2A were simulated using the SOLPS-ITER code. Density scans revealed that when the divertor target electron temperature dropped below 5 eV, a rollover in impurity radiation from the core edge regions of Ar, N, and Ne occurred, and the radiation from impurities in the divertor started to increase concurrently, indicating a correlation between impurity radiation rollover and divertor detachment. Impurity radiation rollover is discovered to be primarily related to impurity transport, which is governed by thermal and friction forces.Prior to divertor detachment, the dominance of thermal forces over friction forces causes impurity ions to transport upstream. However, after detachment, friction forces dominate the impurity ions transport to the divertor region. After analyzing the density and velocity of impurity ions in different charge states, it was found that the core radiation rollover after detachment is mainly caused by high charge state impurity ions. Furthermore, the ability of the divertor to achieve particle flow rollover primarily depends on whether the decrease in plasma pressure ( P t ) exceeds the decrease in plasma temperature ( T t 1 / 2 ).