Modeling Study of Divertor Pumping Effect on Detachment and Impurity Retention with Argon Seeding in EAST

Abstract

The effects of divertor pumping on divertor detachment and core performance are investigated using SOLPS-ITER simulations for the H-mode discharges with argon (Ar) seeding on EAST. The simulation results show that a relatively low pumping speed (S) is advantageous for achieving divertor detachment due to an increased Ar density and enhanced radiative dissipation. On the other hand, a relatively low S results in a high Ar density in the core region, which is detrimental to the core performance. Increasing S improves the particle removal capacity, which is not conducive to obtaining detachment but is conducive to reducing the Ar accumulation in the core region. In order to evaluate the compatibility of detachment and high core plasma performance, the impact of S on the divertor Ar retention (measured by impurity compression C_Ar and enrichment E_Ar) and the corresponding physical mechanisms were analyzed. In cases with relatively low and medium upstream density (\({n}_{\mathrm{e},\mathrm{sep}}^{\mathrm{OMP}}\)), a higher S is beneficial to increase C_Ar and E_Ar, i.e. better core-divertor compatibility, mainly due to the diminished neutral diffusion towards the upstream and the enhanced net force on the Ar towards the target. At relatively high \({n}_{\mathrm{e},\mathrm{sep}}^{\mathrm{OMP}}\), both C_Ar and E_A show no clear change with increasing S. This is because the negative contribution of the reduced relative distance between the Ar ionization front and the velocity stagnation point of the Ar ions to the Ar retention becomes significant with increasing S, which can even offset the positive contribution of the neutral diffusion and the net force.