A quasi-continuous exhaust scenario for a fusion reactor: the renaissance of small edge localized modes

Harrer, G. F.; Faitsch, M.; Radovanovic, L.; Wolfrum, E.; Albert, C.; Cathey, A.; Cavedon, M.; Dunne, M.; Eich, T.; Fischer, R.; Hoelzl, M.; Labit, B.; Meyer, H.; Aumayr, F.; Team, the ASDEX Upgrade; Team, the EUROfusion MST1

doi:10.48550/arxiv.2110.12664

Cited by 2 publications

(2 citation statements)

References 26 publications

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“…H-mode plasma regimes with small ELMs compatible with high density, high confinement, and power exhaust compatible H-mode regimes with small ELMs have been achieved in TCV and AUG [5]. The quasi-continuous exhaust (QCE) regime in AUG is observed with enhanced filamentary transport due to small type-II ELMs and significantly broadened power fall-off length λ q (by a factor up to 4), by operation with increasing fueling [6][7][8]. JOREK simulations have successfully reproduced type-I ELM cycles and the QCE regime in AUG [9].…”

Section: Introductionmentioning

confidence: 98%

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

Li¹,

Xu²,

Wang³

et al. 2022

Nucl. Fusion

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BOUT++ turbulence simulations are conducted for a 60s steady-state long pulse high βp 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 (SOL), 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.

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Section: Introductionmentioning

confidence: 98%

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

Li¹,

Xu²,

Wang³

et al. 2022

Nucl. Fusion

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“…The QCE discharges receive their name from the property of quasi-continuous exhaust, meaning those are discharge without type-I ELMs. The configuration is close to double-null and the separatrix density is high, a combination that allows the pedestal foot to become ballooning unstable [21,22,24]. The selected QCE discharge is the one with HFS fuelling, as it shows a much clearer response in the measured densities, probably because the SOL density shoulder, found in these discharges [25] on the LFS, is responsible for neutral screening.…”

Section: Methodsmentioning

confidence: 99%

Dynamic edge transport investigations at ASDEX Upgrade using gas puff modulation

et al. 2023

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Gas puff modulation experiments are performed at ASDEX Upgrade in L-mode,EDA H-mode and QCE discharges. Plasma density and temperatures are measuredand their temporal development is analyzed simultaneously, revealing that both heatand particle transport are strongly influenced by the modulation. As a consequence,the particle transport coefficients are underdetermined. In the transport modelling,the pedestal cannot be treated as a single region, but the pedestal foot must be allowedto increase its transport with gas puff modulation independently. The analysis of thetemporal behaviours of the heat and particle diffusivities shows that they are stronglycorrelated. Considering the heat diffusivity as a a proxy for the particle diffusivity,allows interpretation of the density evolution: a pinch is not required for any ofthe discharges. An analysis with the gyrokinetic turbulence code GENE identifiesdominant instabilities and reproduces several experimentally found trends. Despite alluncertainties concerning particle transport, one can expect a future reactor featuringa weak edge density gradient even with purely diffusive transport.

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A quasi-continuous exhaust scenario for a fusion reactor: the renaissance of small edge localized modes

Cited by 2 publications

References 26 publications

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

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

Dynamic edge transport investigations at ASDEX Upgrade using gas puff modulation

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