Numerical study of divertor detachment in TCV H-mode scenarios

The effect of divertor closure and nitrogen on the detachment process has been studied by performing 2D numerical simulations of TCV H-mode divertor scenarios with SOLEDGE3X-EIRENE edge plasma transport code. The outcomes reveal that: In the cases with only deuterium gas fuelling, there exists a divertor neutral pressure threshold about 0.76 Pa for detachment, despite the difference in divertor closure. Nitrogen can cool the target temperature with little effect on the upstream density and momentum loss but drops the upstream pressure, leading to a decrease in the target particle flux and divertor neutral pressure. Furthermore, when the radiation front starts to move up from the outer target, the peak parallel heat flux level at the outer target remains approximately the same (about 2.3 MW/m²), despite the difference in nitrogen seeding and divertor closure. An empirical partial detachment qualifier calibrated on AUG experimental data was compared with the TCV simulations. The results show good agreement in detachment state prediction, indicating the potential of this detachment qualifier to be applied in devices of different sizes, emphasizing the combined influence of input power entering the divertor, neutral pressure, and the concentration and species of impurity in achieving divertor detachment.