Experimental study on low recycling no-ELM high confinement mode in EAST

Ye, Y.; Xu, G. S.; Wang, Y.F.; Lin, Xin; Guo, H.Y.; Chen, R.; Niu, Y.; Zhang, T.; Zhou, Chu; Xu, Jichan; Hu, Jiansheng; Sun, Zhuo; Zang, Qing; Yang, Qingquan; Zhu, Ping; Zhang, W.; Wu, Guangming; Zhang, L.; Wang, Li; Shao, L. M.; Hu, G.H.; Li, J.G.; Gao, Xiang; Huang, Jianjun; Wang, Kehuan; Wan, Baonian

doi:10.1088/1741-4326/ab2806

Cited by 16 publications

(12 citation statements)

References 86 publications

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“…More detailed characteristics of these pedestal instabilities on different devices such as the frequency range, mode number, parameter dependence, potential driving source and generating mechanism are well summarized in a series of literatures, i.e. [17,[24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Study on pedestal fluctuations in H-modes without large ELMs during the transition to a detached tungsten divertor in EAST

Yang

Chen

et al. 2021

Nucl. Fusion

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Simultaneous control of the damaging erosion induced by the transient and steady-state heat/particle fluxes on the divertor target material is one of the critical issues for next-step magnetic fusion devices. H-mode operation without large edge-localized modes has been achieved in EAST with an ITER-like tungsten divertor, while being compatible with the partial and pronounced detachment in divertor, via either ramping-up of bulk density or injection of low/high-Z impurities. The pedestal characteristics during the transition from the attached to the detached divertor and the reversed transition (detached to attached) under different detachment methods are studied in detail, where the evolution of multi fluctuating structures commonly residing in the H-mode pedestal of EAST (edge coherent mode (ECM), magnetic coherent mode (MCM) and high frequency mode (HFM)) is highlighted. In addition, the possible mechanisms that affect the behavior of these modes, such as the pedestal pressure gradient and the collisionality, have also been discussed. The radial structures of ECM, MCM and HFM are detected, for the first time, in one discharge. Relevant research may provide contribution to obtaining an integrated small/no ELM and radiative divertor scenario in the next step.

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Section: Introductionmentioning

confidence: 99%

Study on pedestal fluctuations in H-modes without large ELMs during the transition to a detached tungsten divertor in EAST

Yang

Chen

et al. 2021

Nucl. Fusion

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“…In the ELM-free regimes achieved with lithium-wall coating or lithium powder injection in NSTX [19] and DIII-D [20], the pedestal density profile shifts radially inward as well as the peak pressure pedestal gradient region, which helps to stabilize the kink/peeling or ballooning instabilities. The low-recycling no-ELM H-mode regime in EAST [21] is characterized by a low density at the pedestal foot, which helps to strengthen the ion diamagnetic stabilizing effect on the intermediate-n and high-n peeling-ballooning modes (PBMs).…”

Section: Introductionmentioning

confidence: 99%

Grassy ELM regime at low pedestal collisionality in high-power tokamak plasma

Wang

et al. 2020

Nucl. Fusion

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Spontaneous mitigation of giant ELMs and appearance of grassy ELMs have been observed repeatedly at low pedestal collisionality ( ν e , p e d * ∼ 0.15 ) in the high-power (P inj > 13 MW) hybrid scenario in DIII-D. Higher β p and higher q 95 appear to be beneficial to achieving the grassy ELM regime. The grassy ELM H-mode plasma shows high energy confinement performance (H 98y2 up to over 1.5) under the conditions of high neutral beam torque and high core rotation. The pedestal width appears to exceed the EPED1.0 model prediction by more than 50%. Pedestal stability analysis performed with the ELITE code indicates that the stability against low-n kink/peeling modes is improved with increased auxiliary heating power and the operational point in the grassy ELM regime is located near the ballooning boundary. The pedestal stability characteristics during the grassy ELM crashes have been investigated in comparison with the giant ELM crashes based on plasma profiles experimentally measured with high resolution and accuracy. It has been found that the underlying mechanism for the observed small-amplitude ELM crashes is mainly the expansion of the ballooning stability boundary induced by an initial radially localized collapse in the pedestal, which helps to stop the growth of instabilities and further collapse of the pedestal. The effect of electron density pedestal on mitigating edge localized instabilities has been analyzed by numerical simulation, suggesting that the electron density pedestal characterized by high n e,sep/n e,ped and low density gradient helps to stabilize peeling-ballooning modes because of a low pressure pedestal gradient and to lower the ballooning boundary mainly because of a low ion diamagnetic frequency in the pedestal region, thus triggering ballooning instabilities and producing the intrinsic grassy ELMs. Numerical simulation of the Chinese fusion engineering test reactor (CFETR) with the SOLPS code indicates that the separatrix density might be insensitive to the electron diffusivity in the pedestal region and increase with the power flowing from the core region to the edge region. Pedestal stability analysis suggests that the flat density pedestal with high separatrix density obtained in the high-power plasma in CFETR would make the operational point close to the ballooning boundary, which is considered to help destabilize ballooning instabilities and facilitate the access to the grassy ELM regime.

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“…While a direct comparison of pedestal modification and edge stability between Li powder and granule injection is desirable, edge profile data measured by TS during previously published experiments [42] had large statistical errors and cannot be used to construct high fidelity kinetic equilibria needed for ELITE analysis. However, it was reported in a contemporaneous experiment that used a large Li pre-run evaporation coating instead of real-time powder injection, good pedestal profiles were obtained, and the edge stability was analyzed in a discharge transiting from type-III ELMs into an ELM-absent phase [77]. The comparison of profile data between ELMy and ELM-absent phases showed a marked difference in the density profile at the foot of the pedestal; pedestal electron temperature was unaffected.…”

Section: Summary and Discussionmentioning

confidence: 97%

Type-I ELM mitigation by continuous lithium granule gravitational injection into the upper tungsten divertor in EAST

et al. 2021

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Large edge-localized modes (ELMs) were mitigated by gravitational injection of lithium granules into the upper X-point region of the experimental advanced superconducting tokamak (EAST) device with tungsten plasma-facing components. The maximum ELM size was reduced by ∼70% in high β N H-mode plasmas. Large ELM stabilization was sustained for up to about 40 energy confinement times, with constant core radiated power and no evidence of high-Z or low-Z impurity accumulation. The lithium granules injection reduced the edge plasma pedestal density and temperature and their gradients, due to increased edge radiation and reduced recycling from the plasma-facing components. Ideal stability calculations using the ELITE code indicate that the stabilization of large ELMs correlates with improved stability of intermediate-n peeling-ballooning modes, due to reduced edge current resulting from the profile changes. The pedestal pressure reduction was partially offset by a core density increase, which resulted in a modest ∼7% drop in core stored energy and normalized energy confinement time. We surmise that the remnant small ELMs are triggered by the penetration of multiple Li granules just past the separatrix, similar to small ELMs triggered by deuterium pellet Futatani et al (2014 Nucl. Fusion 54 073008). This study extends previous ELM elimination with Li powder injection Maingi et al (2018 Nucl. Fusion 58 024003) in EAST because (1) use of small, dust-like powder and the related potential health hazards were eliminated, and (2) use of macroscopic granules should be more applicable to future devices, due to deeper penetration than dust particles, e.g. inside the separatrix with velocities ∼10 m s−1 in EAST.

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Experimental study on low recycling no-ELM high confinement mode in EAST

Cited by 16 publications

References 86 publications

Study on pedestal fluctuations in H-modes without large ELMs during the transition to a detached tungsten divertor in EAST

Study on pedestal fluctuations in H-modes without large ELMs during the transition to a detached tungsten divertor in EAST

Grassy ELM regime at low pedestal collisionality in high-power tokamak plasma

Type-I ELM mitigation by continuous lithium granule gravitational injection into the upper tungsten divertor in EAST

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