Observations of the effect of lower hybrid waves on ELM behaviour in EAST

Chen, R.; Xu, G. S.; Liang, Y.; Wang, H.Q.; Zhou, Chu; Liu, A.D.; Wang, L.; Qian, Jinping; Gan, Kaifu; Yang, Jie; Duan, You; Li, Y.L.; Ding, Siye; Wu, Xuwen; Niu, Y.; Chen, L.; Shao, L. M.; Zhang, W.; Hu, G.H.; Zhao, Nan; Liu, S.C.; Kong, Defeng; Gong, X.Z.

doi:10.1088/0029-5515/55/3/033012

Cited by 18 publications

(41 citation statements)

References 62 publications

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“…Instead, the perturbations on the edge extreme ultraviolet (XUV) radiation induced by ELMs have been included here. A similar method has been applied in the studies of L-H transition [27] and ELM mitigation by LHCD on EAST [28].…”

Section: Radial Extent Of Perturbations Induced By Small Grassy Elmsmentioning

confidence: 99%

Stationary high-performance grassy ELM regime in EAST

Yang

Niu

et al. 2020

Nucl. Fusion

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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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Section: Radial Extent Of Perturbations Induced By Small Grassy Elmsmentioning

confidence: 99%

Stationary high-performance grassy ELM regime in EAST

Yang

Niu

et al. 2020

Nucl. Fusion

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“…Here, to eliminate the effect of different densities, we normalize the impurity intensity with respect to the centralline-average density n el . The lower impurity concentration is likely due to two effects: (1) no transient heat flux from large ELMs; and (2) improved impurity exhaust, which is probably due to the combined effects of ECM-induced density pump-out and LHCD-induced edge plasma ergodization [15,64].…”

Section: Density and Impurity Controlmentioning

confidence: 99%

A stationary long-pulse ELM-absent H-mode regime in EAST

Wan

et al. 2017

Nucl. Fusion

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A stationary edge-localized mode (ELM)-absent H-mode regime, with an electrostatic edge coherent mode (ECM) which resides in the pedestal region, has been achieved in the EAST tokamak recently. This regime allows the operation of a nearly fully noninductive long pulse (>15 s), exhibiting a relatively high pedestal and good global energy confinement with H 98,y2 near 1.2, and excellent impurity control. Furthermore, this regime is mostly obtained with a 4.6 GHz lower hybrid current drive (LHCD) or counter-current neutral beam injection (NBI), plus electron cyclotron resonance heating, and an extensive lithium wall coating. This stationary ELM-absent H-mode regime transits to a stationary small ELM H-mode regime, and upon additional heating power from the 2.45 GHz LHCD, an ion cyclotron resonant frequency or co-current NBI is applied (under 4.6 GHz LHCD heating background). A slight change of the plasma configuration also makes the small ELMs reappear. The experimental observations suggest that a long-pulse ELM-absent regime can be induced by the ECM, which exhibits strong electrostatic fluctuations and may provide a channel for continuous particle (especially impurities) and heat exhaust across the pedestal. The ECM exists in the collisionality of ν * e = 2.5-4 and the pressure gradient |∇P| = | dP dρ | = 100-200 (kPa), which is in good agreement with the previous simulation of GYRO. This ELM-absent H-mode regime with ECM may offer a suitable candidate for high-performance, steady-state H-mode operation in future fusion reactors.

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“…Numerous efforts have been dedicated to explore the effective techniques for ELM control and many techniques have been developed. Existing methods for ELM control include resonant magnetic perturbations (RMPs) [10][11][12][13][14][15][16][17][18][19][20], supersonic molecular beam injection (SMBI) [8,[21][22][23][24], small pellet pacing [3,[25][26][27][28][29][30], fast vertical jogs of the plasma columns [31,32], and lower hybrid current drive (LHCD) [33][34][35]. ELM control has been achieved with RMPs in JET [14,17], DIII-D [6,10], ASDEX Upgrade [11], MAST [13,16,28], and KSTAR [12,18], with pellet pacing in DIII-D [3] and ASDEX Upgrade [7,[25][26][27][28][29][30], with SMBI in HL-2A [8,…”

Section: Introductionmentioning

confidence: 99%

Control of edge localized modes by pedestal deposited impurity in the HL-2A tokamak

et al. 2018

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Effect of the pedestal deposited impurity on the edge-localized mode (ELM) behaviour has been observed and intensively investigated in the HL-2A tokamak. Impurities have been externally seeded by a newly developed laser blow-off (LBO) system. Both mitigation and suppression of ELMs have been realized by LBO-seeded impurity. Measurements have shown that the LBO-seeded impurity particles are mainly deposited in the pedestal region. During the ELM mitigation phase, the pedestal density fluctuation is significantly increased, indicating that the ELM mitigation may be achieved by the enhancement of the pedestal transport. The transition from ELM mitigation to ELM suppression was triggered when the number of the LBO-seeded impurity exceeds a threshold value. During the ELM suppression phase, a harmonic coherent mode (HCM) is excited by the LBO-seeded impurity, and the pedestal density fluctuation is significantly decreased, the electron density is continuously increased, implying that HCM may reduce the pedestal turbulence, suppress ELMs, increase the pedestal pressure, thus extending the Peeling–Ballooning instability limit. It has been found that the occurance of the ELM mitigation and ELM suppression closely depends on the LBO laser spot diameter.

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Observations of the effect of lower hybrid waves on ELM behaviour in EAST

Cited by 18 publications

References 62 publications

Stationary high-performance grassy ELM regime in EAST

Stationary high-performance grassy ELM regime in EAST

A stationary long-pulse ELM-absent H-mode regime in EAST

Control of edge localized modes by pedestal deposited impurity in the HL-2A tokamak

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