Tungsten erosion and leakage in the new DIII-D V-shaped small angle slot divertor

Validated impurity sourcing and transport simulations of the new tungsten-clad, V-shaped Small Angle Slot (SAS-VW) divertor in the DIII-D tokamak indicate the efficacy of closed, slot-like divertors in containing eroded high-Z impurities. Recent experiments measured a gross tungsten (W) erosion rate halfway between the entrance and bottom of the slot (known as the progressive angle, PA) of 1.3 × 10²⁰ m^-2 s^-1 (T_e ~16 eV, n_e ~2.5 × 10¹⁹ m^-3) with the outer strike point (OSP) at the PA, which decreased by a factor of 3.6 (30% drop in T_e) when the OSP was moved to the slot bottom (ion B × ▽B drift towards the divertor). The observed trend is consistent with DIVIMP impurity transport simulations performed using a SOLPS-ITER plasma background (including particle drift effects), where the average W gross erosion rate calculated at the PA is 8.2 × 10¹⁸ m^-2 s^-1 (T_e ~21 eV, n_e ~1.5 × 10¹⁹ m^-3) when the OSP is on the PA, and decreases by a factor of 54 (71% drop in T_e) when the OSP is moved to the slot bottom. The probability that eroded W leaks into the core is predicted to decrease if sourced closer to the slot bottom, due to an increase in the parallel friction force. Benchmarked modeling of W transport provides valuable guidance for the design of reactor-scale, dissipative divertors.