Title: First snowflake divertor experiments in MAST-U tokamak

Abstract

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 platemore » 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.« less

Authors:

Soukhanovskii, V. A.  ^[1];

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

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+ Show Author Affiliations

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

Publication Date:

Fri Oct 14 00:00:00 EDT 2022

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); Research Council United Kingdom (RCUK); European Atomic Energy Community (EURATOM)

OSTI Identifier:

1894553

Report Number(s):

LLNL-JRNL-836245
Journal ID: ISSN 2352-1791; 1054985; TRN: US2310284

Grant/Contract Number:  

AC52-07NA27344; EP/P012450/1

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Materials and Energy

Additional Journal Information:

Journal Volume: 33; Journal Issue: N/A; Journal ID: ISSN 2352-1791

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; MAST-U snowflake divertor