Modeling deep slot divertor concepts at DIII-D using SOLPS-ITER with drifts

• Published in: Nuclear materials and energy Vol. 34; p. 101356
• Main Authors: Maurizio, R., Leonard, A.W., McLean, A.G., Shafer, M.W., Stangeby, P.C., Thomas, D., Yu, J.H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-03-2023; Elsevier
• Subjects: Detachment; DIII-D; Divertor; Slot divertor; SOLPS-ITER; Detachment; SOLPS-ITER; Slot divertor; DIII-D; Divertor
• ISSN: 2352-1791; 2352-1791
• DOI: 10.1016/j.nme.2022.101356

A staged divertor program is currently under discussion to advance DIII-D research on core-edge integration. One phase could address optimization of power and particle exhaust, and supporting modeling of several slot divertor options is underway, including variations in wall baffling, slot depth and divertor leg length. This paper focuses on the role of slot depth to achieve highly dissipative (detached) divertor conditions, in both BT directions. For ion B×∇B into the divertor and PSOL= 4 MW, SOLPS-ITER finds that increasing the slot depth from 18 to 50 cm reduces the upstream separatrix electron density needed to detach by 15%, due to increased divertor radiation. A dedicated run of the EIRENE neutral transport code, in which neutrals are launched from the outer target and followed until ionization, finds that neutral leakage is strongly reduced in the deep slot compared to the shallow slot, explaining the increased divertor radiation and, thus, lower detachment density threshold. Reversing the BT direction cools and densifies the plasma in the slot, such that both slot options are detached at all simulated densities. As for the opposite BT direction, the deep slot has lower target temperature compared to the shallow slot, as a result of lower neutral leakage. Increasing the depth of a slot divertor is, therefore, beneficial to achieve highly dissipative divertor conditions for both field directions. Additional modeling will build on these results to evaluate whether an increased slot depth can also improve trapping of low-Z radiating impurities.
•A staged divertor program is being discussed to advance DIII-D core-edge integration.•Several slot divertor shapes modeled using SOLPS-ITER with drifts.•This paper discusses the role of slot depth to achieve detached divertor conditions.•A deeper slot (18 to 50 cm) shows reduced detachment density, higher radiation.•Divertor neutral leakage strongly reduced in deeper slot, explains higher radiation.•A deeper slot divertor, thus, shows detachment benefits in both field directions.