SOLPS-ITER modeling study on the impact of mixed impurity seeding on KSTAR tungsten divertor plasma

A SOLPS-ITER modeling study is performed to estimate the influence of mixed nitrogen (N) and neon (Ne) seeding on the KSTAR tungsten divertor plasma. Individual scan with either N or Ne seeding rate exhibits a clear transition from attached to partially detached regime for 5 MW of heating power case based on the H-mode shot with the first impurity injection test in the KSTAR tungsten divertor commissioning. For individual impurity seeding cases, Ne radiates in the pedestal region stronger than N, resulting in potential issues with sustaining good H-mode performance. An impurity mixture with complementary radiative loss parameters is expected to promote efficient radiation across a broader temperature range, reducing fuel dilution for the same radiation level. For the impurity mixture of N and Ne, a coarse scan is performed by gradually increasing the proportion of N in the impurity mixture for the same total impurity seeding rates. Simulation results are analyzed in terms of the divertor neutral pressure and impurity concentration at the separatrix. A Ne seeding rate of approximately 25% of the N seeding rate achieves similar levels of divertor neutral pressure. The mixture of N and Ne reduces fuel dilution without reducing the degree of detachment. Understanding multi-impurity plasmas will support better detachment/dissipation control in experiments.