How fluctuation intensity flux drives SOL expansion

Li, Nami; Xu, X.Q.; Diamond, P.H.; Zhang, T.; Liu, X.; Wang, Y.F.; Yan, N.; Xu, G.S.

doi:10.1088/1741-4326/ad0599

Cited by 6 publications

(1 citation statement)

References 35 publications

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“…The grassy-ELM λ js is larger than the inter large-ELM λ js is probably due to that the turbulence in pedestal is largely suppressed during the inter-ELM phase and strong turbulent fluctuations for the grassy-ELM pedestal enhance the cross-field transports of particles and heat into the SOL, which should broaden λ js in principle. This is supported by BOUT++ 3D turbulence simulations in the recent study [40]. To further confirm this theory, dedicated experiments with sufficient diagnostic measurements in the edge and SOL are required.…”

Section: Comparison Of the Sol Particle Flux Width For Different Elm ...mentioning

confidence: 58%

Experimental scalings of scrape-off layer particle flux width by outboard divertor Langmuir probes for deuterium and helium plasmas on EAST

Liu,

Meng,

et al. 2023

Nucl. Fusion

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The scrape-off layer (SOL) power width (λq ) is an important parameter for predicting the heat load on divertor targets for future magnetically confined devices. Currently, the underlying physics for λq scaling is not fully understood. This paper extends the previous SOL particle flux width (λjs, λq ≈ λjs is assumed, js is the measured ion current density used as a proxy for particle flux) scaling measured by the inboard divertor Langmuir probes (Div-LPs) in deuterium plasmas (Liu et al 2019 Plasma Phys. Control. Fusion 61 045001) to the λjs scalings measured by the outboard Div-LPs in both deuterium and helium plasmas on EAST. A systematic method has been used to correct the upper-outer Div-LP measurements to reduce the measurement uncertainty of λjs . About 520 discharges are selected for the construction of six databases (H-mode, L-mode, and Ohmic for deuterium and helium plasmas) to scale λjs . Since the published λq scalings do not fit EAST λjs well in the databases, four separate λjs scalings are proposed using statistical method to minimize the scaling parameters. It is found that λjs has a robust scaling dependence on the plasma line-averaged density ( n ˉ e ) for both deuterium and helium plasmas and a strong positive scaling dependence on the divertor leg length (L div,leg). The scaling exponent of the stored energy agrees well with the previous λq /λjs scalings for deuterium plasmas. The near unity scaling exponents of edge safety factor and L div,leg reveal the importance of parallel connection length in determining λjs . The positive scaling dependence of λjs on n ˉ e and the 2 ∼ 4 times larger scaling amplitude compared with the published λq scalings probably indicate the turbulence broadening of λjs on EAST. The comparison of λjs for deuterium and helium plasmas using the constructed databases shows no significant difference. Statistical comparison of the normalized λjs with different ELM types suggests that the grassy-ELM λjs is slightly larger than the inter large-ELM (type-I ELM) λjs for both deuterium and helium plasmas.

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Section: Comparison Of the Sol Particle Flux Width For Different Elm ...mentioning

confidence: 58%

Experimental scalings of scrape-off layer particle flux width by outboard divertor Langmuir probes for deuterium and helium plasmas on EAST

Liu,

Meng,

et al. 2023

Nucl. Fusion

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Turbulence spreading effects on the ELM size and SOL width

Li,

Xu,

Diamond

et al. 2024

J. Plasma Phys.

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BOUT++ turbulence simulations were performed to investigate the impact of turbulence spreading on the edge localized mode (ELM) size and divertor heat flux width $({\lambda _q})$ broadening in small ELM regimes. This study is motivated by EAST experiments. BOUT++ linear simulations of a pedestal radial electric field (Er) scan show that the dominant toroidal number mode (n) shifts from high-n to low-n, with a narrow mode spectrum, and the maximum linear growth rate increases as the pedestal Er well deepens. The nonlinear simulations show that as the net E × B pedestal flow increases, the pressure fluctuation level and its inward penetration beyond the top of the pedestal both increase. This leads to a transition from small ELMs to large ELMs. Both inward and outward turbulence spreading are sensitive to the scrape-off-layer (SOL) plasma profiles. The inward turbulence spreading increases for the steep SOL profiles, leading to increasing pedestal energy loss in the small ELM regime. The SOL width $({\lambda _q})$ is significantly broadened progressing from the ELM-free to small ELM regime, due to the onset of strong radial turbulent transport. The extent of the SOL width $({\lambda _q})$ broadening depends strongly on outward turbulence spreading. The fluctuation energy intensity flux ${\varGamma _\varepsilon }$ at the separatrix can be enhanced by increasing either pedestal Er flow shear or local SOL pressure gradient. The ${\lambda _q}$ is broadened as the fluctuation energy intensity flux ${\varGamma _\varepsilon }$ at the last close flux surface (LCFS) increases. Local SOL E × B flow shear will restrain outward turbulence spreading and the associated heat flux width broadening. Operating in H-mode with small ELMs has the potential to solve two critical problems: reducing the ELM size and broadening the SOL width.

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How turbulence spreading improves power handling in quiescent high confinement fusion plasmas

Li,

Chen,

Diamond

et al. 2024

Commun Phys

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Viable magnetic fusion devices necessitate combining good confinement with effective power flux handling. A major concern for ITER, and devices beyond, is the divertor heat load width, which sets peak boundary heat loads on the plasma-facing materials. Current estimates of the heat flux width are narrow for future reactors. Here, we demonstrate how pedestal turbulence can expand into, or entrain, the stable scrape-off-layer and so broaden the heat flux width beyond these neoclassical predictions. Employing combined theoretical, computational, and experimental approaches, we focus on quiescent high confinement discharges on the DIII-D tokamak, but the results are of broader significance. Our findings uncover common trends in the edge turbulence intensity flux, the pressure perturbation skewness, and the turbulence mixing length, which together determine the heat flux width. This research demonstrates the physics of scrape-off-layer broadening by turbulence and highlights the promise of a turbulent pedestal for successful core-edge integration in ITER and future fusion devices.

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How fluctuation intensity flux drives SOL expansion

Cited by 6 publications

References 35 publications

Experimental scalings of scrape-off layer particle flux width by outboard divertor Langmuir probes for deuterium and helium plasmas on EAST

Experimental scalings of scrape-off layer particle flux width by outboard divertor Langmuir probes for deuterium and helium plasmas on EAST

Turbulence spreading effects on the ELM size and SOL width

How turbulence spreading improves power handling in quiescent high confinement fusion plasmas

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