Design of a new closed divertor for negative triangularity operation in DIII-D

A new closed, pumped divertor is designed for the DIII-D tokamak to improve core-edge compatibility of Negative Triangularity (NT) scenarios. Discharges with strong NT shaping in the armor campaign required high density (f_Gw~1.3) to achieve detachment with intrinsic radiation due to limited divertor volume and short connection length. Confinement degradation was observed with increasing density, and MARFE formation affected confinement after detachment. A new divertor is being designed for installation in DIII-D, optimized for shapes with intermediate NT ( δ~-0.3) with longer parallel connection lengths (2.5x) and poloidal leg length (2x) compared to strong NT, and access to divertor pumping. The intermediate NT prevents access to second stability in simulations, ensuring ELM-free operation. Closed divertor plasma-facing components with private flux region pumping were optimized to reduce detachment onset density and improve particle control. SOLPS-ITER and UEDGE simulations show a reduction in detachment onset density due to the plasma geometry by about 30%, with further reduction enabled by the outer vertical target. Simulations show higher T_e at the X-point before the onset of detachment in the new geometry, reducing confinement degradation when approaching detachment.