Characteristics of toroidal rotation and ion temperature pedestals between ELM bursts in KSTAR H-mode plasmas

Ko, S. H.; Kwon, Jae Min; Ko, W. H.; Kim, S. S.; Jhang, Hogun; Terzolo, L.

doi:10.1063/1.4953425

Cited by 4 publications

(2 citation statements)

References 57 publications

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“…We find that the effective Prandtl number reaches about 0.35 and 0.24 for D and He bulk plasmas, respectively. This is comparable to experimentally observed effective Prandtl numbers in the plasma core of JET 37 and KSTAR 38 . Since experimental ion heat transport can be comparable to the neoclassical predictions in a pedestal 39 , assuming that our results extrapolate to large temperature gradient, we may expect finite orbit width effects to significantly contribute to the total momentum transport in a pedestal 3 .…”

Section: B Fixed φ Radial Flows and Fluxessupporting

confidence: 88%

Neoclassical flows in deuterium–helium plasma density pedestals

Buller¹,

Pusztai²,

Newton³

et al. 2017

Plasma Phys. Control. Fusion

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In tokamak transport barriers, the radial scale of profile variations can be comparable to a typical ion orbit width, which makes the coupling of the distribution function across flux surfaces important in the collisional dynamics. We use the radially global steady-state neoclassical δf code Perfect to calculate poloidal and toroidal flows, and radial fluxes, in the pedestal. In particular, we have studied the changes in these quantities as the plasma composition is changed from a deuterium bulk species with a helium impurity to a helium bulk with a deuterium impurity, under specific profile similarity assumptions. The poloidally resolved radial fluxes are not divergence-free in isolation in the presence of sharp radial profile variations, which leads to the appearance of poloidal return-flows. These flows exhibit a complex radial-poloidal structure that extends several orbit widths into the core and is sensitive to abrupt radial changes in the ion temperature gradient. We find that a sizable neoclassical toroidal angular momentum transport can arise in the radially global theory, in contrast to the local.

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Section: B Fixed φ Radial Flows and Fluxessupporting

confidence: 88%

Neoclassical flows in deuterium–helium plasma density pedestals

Buller¹,

Pusztai²,

Newton³

et al. 2017

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

show abstract

“…The decrease in V tor,e may stem from either increased toroidal momentum transport, like in the case of n e , or reduced residual stress while with a similar external momentum input. Note that residual stress is known to be the primary toroidal momentum source in the edge region in KSTAR H-mode discharges [39] and is highly reliant on the pedestal structure. Therefore, pedestal broadening in the high-performance case, as represented in section 2.2, may cause a reduction in V tor,e .…”

Section: Overview Of the Similar High-and Low-performance Dischargesmentioning

confidence: 99%

Effect of coherent edge-localized mode on transition to high-performance hybrid scenarios in KSTAR

Lee,

Kim,

Kim

et al. 2023

Nucl. Fusion

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This paper deals with one of the origins and trigger mechanisms responsible for the observed performance enhancements in the hybrid scenario experiments conducted in Korea Superconducting Tokamak Advanced Research (KSTAR). The major contribution to the performance improvement comes from the broader and higher pedestal formation. The increase of fast ion pressure due to the plasma density decrease also contributes substantially to the global beta. Although the reduced core plasma volume resulting from the pedestal expansion has a negative effect on the core thermal energy, a considerable confinement improvement observed in the inner core region limits the degradation. The one significant characteristic of high-performance discharges is the presence of coherent edge-localized mode (CEM) activity. CEM is triggered during the pedestal recovery phase between typical ELM crashes and has been found to be related to the increase of particle and heat transport. It appears to underlie two commonly observed phenomena in high-performance hybrid scenario discharges in KSTAR: pedestal broadening and continuous density decrease. Despite the associated transport increase, CEM activities can induce performance enhancement. With the pedestal broadening, ELM crashes become delayed and weakened, which, in turn, allows for a higher pedestal. Moreover, the density decrease directly increases fast ion pressure by extending the beam-slowing-down time. The linear gyrokinetic analysis reveals that the increase of fast ions could initiate positive feedback loops, leading to the stabilization of ion temperature gradient mode (ITG) in the inner core region.

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BOUT++ nonlinear simulation for a comparative study with the measured 2D ELM structures in the KSTAR H-mode plasma

et al. 2019

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Time-dependent nonlinear simulation using the BOUT++ 3-field model is performed for a study of edge localized mode (ELM) dynamics in KSTAR H-mode plasmas. The simulated results of the ELM evolution are directly compared with the 2D ELM structures, measured by electron cyclotron emission imaging systems, from the initial growth to crash phase. The simulation results are qualitatively in good agreement with the observations. Specifically, it is notable in simulation and experiment that higher-n modes in a quasi-steady state phase evolve into lower-n modes close to the ELM-crash in time. It suggests that lower-n modes may be responsible for the onset of the crash. A postanalysis supports that nonlinear mode coupling between toroidal harmonics may drive the lower-n mode.

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Characteristics of toroidal rotation and ion temperature pedestals between ELM bursts in KSTAR H-mode plasmas

Cited by 4 publications

References 57 publications

Neoclassical flows in deuterium–helium plasma density pedestals

Neoclassical flows in deuterium–helium plasma density pedestals

Effect of coherent edge-localized mode on transition to high-performance hybrid scenarios in KSTAR

BOUT++ nonlinear simulation for a comparative study with the measured 2D ELM structures in the KSTAR H-mode plasma

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