Multi-scale interaction of pedestal instabilities in H-mode plasma on the EAST tokamak

Zhang, T.; Geng, Kangning; Liu, H.Q.; Liu, Y.; Shi, Tonghui; Duan, Yanmin; Liu, J.B.; Xiang, Haoming; Wang, Y. M.; Wen, Fei; Li, G.S.; Ye, K.X.; Wu, Mengfan; Huang, J.; Zhang, S.B.; Gao, Xiang

doi:10.1088/1741-4326/ab0755

“…For the EAST tokamak, the density inversion method for lithium beam probe is under optimization. The ECE system can only provide reliable pedestal top temperature even though there is no fast-electron interference induced by LHCD (due to the quick drop in optical thickness in the pedestal [25,26]). Instead, the perturbations on the edge extreme ultraviolet (XUV) radiation induced by ELMs have been included here.…”

Section: Radial Extent Of Perturbations Induced By Small Grassy Elmsmentioning

confidence: 99%

Stationary high-performance grassy ELM regime in EAST

Yang

¹

,

Xu

²

,

Niu

³

et al. 2020

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A stationary, high-performance grassy edge-localized mode (ELM) regime has been successfully accessed on the EAST tokamak since the 2016 campaign. increase via increase of heating power or q95 are both found to facilitate a higher grassy ELM frequency. Edge measurement of absolute extreme ultraviolet radiation indicates that the affected area by grassy ELMs is localized at the pedestal region and the perturbations there induced by grassy ELMs can be 90% smaller than that by type-I ELMs. Parameter scan demonstrates that the grassy ELM regime has good density control capacity, and the access to the grassy ELM regime is independent of the toroidal field direction and low-hybrid-wave power. Statistical analysis indicates that the grassy ELM regime is highly reproducible in a wide parameter space when edge safety factor and poloidal beta are simultaneously high enough ( and ). High triangularity contributes to the increase of grassy ELM frequency while the requirement on high internal inductance in the JET tokamak for grassy ELMs cannot be found in EAST. The operational space in pedestal top collisionality for the EAST grassy ELMs is in the range of . The exploration towards lower is mainly limited by the available heating power. Evolution of a coherent mode at pedestal top suggests that grassy ELMs most likely generate in the steep-gradient region of the pedestal, rather than on the pedestal top or near the separatrix. The grassy ELM regime offers a highly promising approach for further exploration of long-pulse high-performance H-mode operations in EAST, with potential application to the Chinese Fusion Engineering Test Reactor (CFETR) as the baseline scenario and a primary solution for the control of ELMs.

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“…Tearing modes modulate turbulence and the plasma flow in the plasma core, as reported in tokamaks [16][17][18][19][20][21]. Furthermore, there are investigations of turbulence coherent structures modulated by the kink instability and micro-turbulence modulated by the lowfrequency mode (LFM) in the H-mode pedestal region [22,23]. Turbulence and plasma flows are known to be modulated by MHD modes in different confinement regimes and regions indicating common features of cross-scale interaction, which is of significant importance for further study in order to find possibilities to control turbulence and induced transport.…”

Section: Introductionmentioning

confidence: 92%

Investigation of a low frequency coherent mode in Wendelstein 7-X with island divertor

Xiang,

Krämer-Flecken,

Han

et al. 2023

Nucl. Fusion

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During the island divertor operation of W7-X especially in standard magnetic configuration (with 5/5 island chain in the scrape-off-layer (SOL)), a quasi- periodic electromagnetic oscillation is observed. It appears in the frequency range of 1 kHz to 2 kHz, therefore it is called low frequency mode (LFM) within this paper. It is observed by multiple diagnostics, amongst them, a poloidal correlation reflectometer (PCR) allowing a radial localization of LFM. The LFM localized in SOL and shows an obvious modulation effect on the plasma perpendicular velocity (V⊥). Furthermore, broadband turbulence observed in the fluctuation spectra of the electron density and the magnetic field, and the perpendicular correlation length of turbulence eddies, are modulated. The calculation of the poloidal flow velocity and its oscillation allows to study the affect of the LFM on the flow. Cross correlation analysis shows that the perpendicular flow oscillation and the turbulence modulation are closely correlated. The application of external control coils to adjust the island size and position, result in a strong modification of the magnetic topology at the plasma edge which affects the appearance, amplitude and frequency of LFM. Bi-cohernece analysis indicates that a nonlinear interactions among turbulence components is a possible mechanism for the generation of LFM.

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“…It was found that the pedestal width of EAST ELMy H-modes is wider than that of DIII-D but there is also a good correlation with the square root of pedestal poloidal beta β 1/2 p,ped [19]. The experimental studies found that the appearance and disappearance of the CM was correlated to the pedestal pressure on EAST [22,25]. This article mainly focuses on the preliminary research on the pedestal width and height of the selected H-mode discharges, and further try to use the REPED model to predict the pedestal height for EAST H-mode plasmas.…”

Section: Introductionmentioning

confidence: 95%

Study of H-mode pedestal predictive model on EAST tokamak

Li¹,

Li²,

Zang³

et al. 2020

Plasma Phys. Control. Fusion

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The pedestal structure of the high-confinement mode (H-mode) operation strongly impacts global confinement and fusion performance in tokamak devices. Studies of the pedestal structure also play an important role in better understanding the characterization of H-mode plasma discharges with type-I edge localized modes on the Experimental Advanced Superconducting Tokamak (EAST). The EPED model has been widely validated to predict the pedestal structure of several tokamak devices. The mean pedestal width Δ ψ correlates with the square root of the poloidal pedestal beta β p , p e d 1 / 2 and is in good agreement with Δ ψ = 0.12 β p , p e d 1 / 2 from experimental observations. It is also found that the scaling coefficients of Δ ψ and β p , p e d 1 / 2 may have no dependence on the heating schemes. The comparison of predictions with measurements indicates that the REPED model could be used to predict the pedestal height for a range of experimental pedestal pressures (

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Multi-scale interaction of pedestal instabilities in H-mode plasma on the EAST tokamak

Cited by 7 publications

References 43 publications

Stationary high-performance grassy ELM regime in EAST

Stationary high-performance grassy ELM regime in EAST

Investigation of a low frequency coherent mode in Wendelstein 7-X with island divertor

Study of H-mode pedestal predictive model on EAST tokamak

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