Characteristics of grassy ELMs and their impact on the divertor heat flux width

Li, Nami; Xu, X. Q.; Wang, Y. F.; Yan, N.; Zhang, J. Y.; Qian, J. P.; Sun, J. Z.; Wang, D. Z.

doi:10.1088/1741-4326/ac83d9

Characteristics of grassy ELMs and their impact on the divertor heat flux width

Journal Article · Tue Aug 16 00:00:00 EDT 2022 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac83d9· OSTI ID:1893604

^[1]; Xu, X. Q. ^[2]; ^[3]; ^[3]; Zhang, J. Y. ^[3]; Qian, J. P. ^[3]; ^[4]; ^[4]

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Dalian University of Technology (China)
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Chinese Academy of Sciences (CAS), Hefei (China)
Dalian University of Technology (China)

We report BOUT++ turbulence simulations are conducted for a 60 s steady-state long pulse high β_p EAST grassy ELM discharge. BOUT++ linear simulations show that the unstable mode spectrum covers a range of toroidal mode numbers from low-n (n = 10–15) peeling–ballooning modes (P–B) to high-n (n = 40–80) drift-Alfvén instabilities. Nonlinear simulations show that the ELM crash is triggered by low-n peeling modes and fluctuation is generated at the peak pressure gradient position and radially spread outward into the scrape-off-layer, even though the drift-Alfvén instabilities dominate the linear growth phase. However, drift-Alfvén turbulence delays the onset of the grassy ELM and enhances the energy loss with the fluctuation extending to pedestal top region. Simulations further show that if the peeling drive is removed, the fluctuation amplitude drops by an order of magnitude and the ELM crashes disappear. The divertor heat flux width is ~2 times larger than the estimates based on the HD model and the Eich's ITPA multi-tokamak scaling (or empirical Eich scaling) due to the strong radial turbulence transport.

View Accepted Manuscript (DOE)

Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); National Key R&D Program of China; Chinese Academy of Science (CAS); National Natural Science Foundation of China

Grant/Contract Number:: AC52-07NA27344

OSTI ID:: 1893604

Report Number(s):: LLNL-JRNL-833914; 1052270

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 9 Vol. 62; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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