Abstract Details
| status: | file name: | submitted: | by: |
|---|---|---|---|
| approved | namili_sherwood2023_abstract_v0.pdf | 2023-03-24 13:21:24 | Nami Li |
Abstracts
Author: Nami Li
Requested Type: Consider for Invited
Submitted: 2023-03-20 18:16:57
Co-authors: X.Q. Xu, P.H. Diamond, Y.F. Wang, X. Lin, N. Yan and G.S. Xu
Contact Info:
Lawrence Livermore National Laboratory
7000 East Ave.
Livermore, CA 94550
USA
Abstract Text:
Simultaneously controlling large ELMs and divertor heat loads in H-mode plasma is crucial for achieving steady-state operation of a tokamak fusion reactor. Both experiments and simulations have shown that H-mode plasma regimes with small/grassy ELMs can help to reduce the ELM size and broaden the SOL width λ_q, while maintaining high plasma confinement compared to type-I ELMs. BOUT++ turbulence simulations were conducted to investigate the effects of turbulence spreading on λ_q broadening in small ELM regimes. This study is motivated by 4 EAST discharges with 2 different poloidal magnetic field B_p in small ELMs, where the pedestal is near marginal stability and relaxes into a linearly stable state after the initial ELM crash. BOUT++ nonlinear simulations have shown that turbulence energy intensity flux Γ_ε is a crucial factor in the broadening of the SOL width λ_q. λ_q is broadened as fluctuation energy intensity flux Γ_ε at last close flux surface (LCFS) increases due to increasing pedestal ExB flow shear and local SOL turbulence. The transition from ELM-free to small ELM regime leads to a significant broadening of the SOL width (λ_q) due to the strong radial transport of turbulence energy. This has been confirmed by EAST experiment. The spreading of turbulence from the pedestal to the SOL is highly dependent on the pedestal plasma parameters. As the pedestal pressure gradient ∇P_0 increases and the pedestal collisionality υ_ped^* decreases, the fluctuation energy intensity flux Γ_ε also increases. Furthermore, the radial mode extension for low-n peeling modes is wider than that of high-n ballooning modes, leading to a higher energy intensity flux Γ_ε for low collisionality υ_ped^*. Operating in H-mode with small ELMs has tremendous potential to address two of the most critical problems for Tokamak fusion reactors: significantly reducing the ELM size and substantially broadening the SOL width.
Comments: