First snowflake divertor experiments in MAST-U tokamak

Journal Article · Fri Oct 14 00:00:00 EDT 2022 · Nuclear Materials and Energy

DOI:https://doi.org/10.1016/j.nme.2022.101278· OSTI ID:1894553

Soukhanovskii, V. A. ^[1]; Cunningham, G. ^[2]; Harrison, J. R. ^[2]; Federici, F. ^[2]; Ryan, P. ^[2]

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1. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
2. Culham Centre for Fusion Energy (CCFE) (United Kingdom)

First snowflake (SF) divertor experiments in the MAST-U tokamak demonstrated steady-state snowflake-plus divertor configurations in 450 kA ohmic L-mode plasmas. The SF divertor configuration features a second poloidal field (PF) null in the divertor region close by or overlapping with the main X-point. The resulting low PF region and two additional divertor legs (strike points) may lead to additional power and particle flux sharing via a hypothesized convective cell, and increased plasma-wetted area and radiation. The free-boundary Grad–Shafranov equilibrium code FIESTA was used to design SF configurations with several inter-null distances and orientations. In the experiment, the SF configurations with inter-null distances 0.13–0.20 m and lasting 0.2–0.3 s were obtained. Parallel connection lengths between the midplane and the outer strike point in the SF configurations (evaluated at field lines 1–2 mm from the separatrix in the midplane) were 25–30 m, higher than in the standard divertor (20–25 m) or the Super-X divertor (25 m). Diagnostic measurements highlighted salient SF features. The infra-red video bolometer diagnostic showed that the radiated power peaking in the PF null region was not as pronounces as in the standard divertor. Divertor ion fluxes measured by target Langmuir probes showed increased ion flux in the plate region where a secondary SF strike point landed, concomitantly with the SF formation. These measurements may suggest that some particle and heat redistribution was taking place in the convective SF zone. The first SF experiments provide a basis for future SF studies in MAST-U tokamak with higher input power, improved plasma control and diagnostic measurements, to be compared with the modeling predictions of plasma convective SF mixing and lower density strike point detachment threshold.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: European Atomic Energy Community (EURATOM); Research Council United Kingdom (RCUK); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1894553
• Report Number(s): LLNL-JRNL-836245; 1054985
• Journal Information: Nuclear Materials and Energy, Journal Name: Nuclear Materials and Energy Journal Issue: N/A Vol. 33; ISSN 2352-1791
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
MAST-U snowflake divertor