First SOLPS-ITER Simulations of an X-point Radiator in the DIII-D High-beta Hybrid Plasmas

For the first time in DIII-D, drift-dependent SOLPS-ITER modeling is able to qualitatively reproduce the measured plasma conditions with an X-point radiator (XPR) using a high-beta hybrid scenario. It highlights the key role of neutrals, drifts, divertor closure and efficient pumping in the formation of an XPR. A series of interpretive simulations were conducted to capture the XPR dynamics and advance the current understanding of XPR physics. As the seeding rate of N₂ increases in the modeling, the radiation zone moves away from the outer target towards upstream and eventually above the X-point. In the meantime, the electron temperature near the X-point quickly drops below 5eV along with significantly increased X-point neutral density by over an order of magnitude. The drift flows are comparable with the parallel flow and strongly affect the impurity distribution, leading to radiation peak on the low-field side, which is consistent with the Bolometer and TangTV measurements. SOLPS-ITER also predicts that in an open divertor configuration, even when the radiation front moves above the X-point, complete detachment is not achieved at the target, which is consistent with experimental observation. Divertor geometry strongly affects the distribution of neutrals and drift flow pattern, and thus the impurity distribution. This modeling further fills the gaps between the experiments and theoretical analysis, providing a better understanding of the operation window and access condition of XPR in DIII-D.