Tungsten–carbon surface evolution and erosion modeling for a small angle slot divertor in DIII-D

Journal Article · 24 November 2021 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ac36f4 · OSTI ID:1832613

Brooks, J. N.; Sizyuk, T. ; Sinclair, G. ; Hassanein, A.

Abstract We modeled tungsten–carbon mixed surface evolution, sputtering erosion, and transport for the tungsten coated region of a small angle slot (SAS) divertor design for the DIII-D tokamak. This divertor concept aims to achieve a closed slot dissipative plasma to minimize heat load and surface erosion, and to study high- Z material performance. Our advanced simulations use coupled ITMC-DYN material mixing/response and 3D full kinetic REDEP/WBC erosion/redeposition code packages, with divertor plasma solution from the SOLPS-ITER package with 4 MW power input. The SAS design geometry and resulting in-slot plasma parameters cause significant differences in predicted sputter/transport from a conventional divertor. For 2% C/D incident plasma ratio, an equilibrium mixed C/W surface is attained at ∼30 s of discharge, from wall sputtered carbon transported to the 10 cm long tungsten divertor region. Tungsten remains exposed to the plasma, but the evolved surface composition varies with different C/D ratios. Tungsten is primarily sputtered from the mixed surface by impinging carbon ions in the +1 to +4 charge states, with some self-sputtering. Redeposition of sputtered tungsten to the divertor is significant, ∼80% along the higher plasma temperature attached plasma SAS entrance region, but this is less than the typically near-unity values for a conventional divertor. Plasma-incident carbon is highly backscattered (∼50%) from the mixed surface, with little redeposition (<10%); this helps maintain tungsten in the surface sputter zone. Carbon is mainly sputtered from the mixed surface by D ⁺ ions, also with low redeposition (∼10%–30%). Finally, the modeling shows non-zero but low sputtered tungsten current from the divertor to the core plasma direction. These results appear favorable for effective testing of a tungsten-containing SAS divertor in DIII-D, and extrapolation of mixed-material evolution/response findings to the analogous low- Z /high- Z , Be/W, ITER plasma facing system.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States); General Atomics, San Diego, CA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: AC02-06CH11357; FC02-04ER54698; SC0020198
• OSTI ID: 1832613
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 12 Vol. 61; ISSN 0029-5515
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: IAEA
• Language: English