Experimental observation of coexisting electromagnetic fluctuations correlating with the inter-ELM pedestal evolution on EAST

Lan, H.; Chen, R.; Xu, G. S.; Niu, Y.; Chen, L.; Zhang, H.; Ye, Y.; Lan, Tao; Sun, P. J.; Xu, Jichan; Lin, Xin; Wang, Y. F.; Yang, Qingquan; Zhao, Hailin; He, Kang; Shi, Tonghui; Wang, Y. M.; Zang, Qing; Liu, Haiqing; Duan, Yanmin; Chen, Y. J.; Meng, Lingyi; Zhou, Chu; Li, Y. Y.; Zhang, W.; Wang, Li; Zhou, Tianfu

doi:10.1063/1.5123734

Cited by 11 publications

(19 citation statements)

References 86 publications

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“…The experimental results indicate that the low-frequency coherent mode with n = 1 is localized at the edge [52,53], so we explore this branch mode in the simulation. The corresponding results are shown in figures 10 and 11 using the kinetic model with all terms in equation ( 2).…”

Section: Simulation Resultsmentioning

confidence: 99%

Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

et al. 2021

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Multiple electromagnetic coherent modes with frequencies f ∼ 20–300 kHz and toroidal mode numbers n = 1 and n = 2 have been observed and investigated in radio-frequency heated H-mode plasmas of the EAST tokamak. The experimental results show that the two main branches of these coherent modes are driven by energetic electrons (EEs), which are produced in the processes of radio-frequency current drive and heating. Bicoherence analysis indicates that there are strong nonlinear mode interactions between the two branches (mother waves), i.e. one is in the low-frequency range of f ∼ 20–50 kHz and the other one is in the high-frequency range of f ∼ 120–250 kHz, and their nonlinear couplings can generate many harmonics (daughter waves). Both coherent modes propagate poloidally along the electron diamagnetic drift direction. The gyrokinetic eigenvalue simulations support the view that both the low-frequency and the high-frequency coherent modes observed in EAST are Alfvén eigenmode (AE) type, and the kinetic effects of background plasmas and EEs are responsible for the formation and excitation of AEs, respectively. The low-frequency coherent mode is identified as the kinetic beta-induced Alfvén eigenmode located in the edge, and the high-frequency coherent mode is radially global, which is characterized by a toroidal Alfvén eigenmode (TAE) in the core and also has the components of a kinetic TAE and ellipticity-induced Alfvén eigenmode in the outer region due to the large downshift of the Alfvén continuum gap from the core to the edge in H-mode discharges.

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Section: Simulation Resultsmentioning

confidence: 99%

Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

et al. 2021

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“…Therefore, the simulation results only considering the experimental profiles are not consistent with the insignificant ELM experiment. There must be some other key factors missed, such as the interactions between the CM and ELMs [14].…”

Section: The Experiments and Analysismentioning

confidence: 99%

“…The CMs have been discovered at the boundary of plasma in tokamak devices [14]. When CM is present, it is often accompanied by the ELM mitigation and suppression.…”

Section: Introductionmentioning

confidence: 99%

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

Li¹,

Xia²,

Zou³

et al. 2022

Nucl. Fusion

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A general phenomenon that the edge localized modes (ELMs) can be effectively mitigated with the enhanced coherent modes (CMs) has been observed on EAST. For this phenomenon, the experimental statistical analysis and electromagnetic (EM) simulations have been performed. There is a threshold value of the CM intensity in the experiments, which plays a key role in ELMs mitigation. Through the ELITE and conventional BOUT++ analysis, we found that when the insignificant ELM and enhanced CM co-exist, the pedestal is located in unstable P-B region and the ELM is relatively large. The simulation results only using the experimental profiles without considering other factors cannot reproduce the no significant ELM experiment. The CM enhances the edge turbulence, which can control ELMs. Therefore, the effects of CM are considered to explain the ELM mitigation. Modifying the three-field reduced model in BOUT++, an imposed perturbation is added as the CM. The simulation results indicate that: without the CM, the ELM size belongs to the relative large ELM region; after considering the CM, the ELM is mitigated and the energy loss is reduced by about 44.5%. Analysis shows that the CM enhances the three-wave nonlinear interactions in the pedestal and reduces the phase coherence time (PCT) between the pressure and potential, which lead the perturbation to tend to be ‘multiple-mode’ coupling. The competition of free energy between the multiple modes leads to the lack of obvious filament structures and the decreased energy loss. The above reveals that there is a competitive relationship between turbulence and ELMs, and the CM-enhanced turbulence can effectively reduce ELM energy loss. In addition, through the parameter scanning, there is a threshold of the amplitude A, which is consistent with the statistical results in the experiments.

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“…In EAST, a lot of coherent modes have also been observed, including the edge electrostatic coherent mode (ECM) with the frequency range of 20-90 kHz [18], broadband fluctuations with the frequency range of 0-200 kHz [19], and magnetic coherent mode with the frequency range of 20-60 kHz [20]. These fluctuations can exist alone or simultaneously during the inter-ELM period [21], and propagate in the electron diamagnetic drift direction in the laboratory frame or plasma frame and correlate with the pedestal density or pressure evolution. Lately, a variety of experimental studies on pedestal localized fluctuations inter-ELM period across several tokamaks have been reviewed and summarized [22].…”

Section: Introductionmentioning

confidence: 99%

Global gyrokinetic simulation of edge coherent mode in EAST

Xie

Chen

et al. 2023

Nucl. Fusion

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Linear and nonlinear simulations are carried out for the edge coherent mode (ECM) using the global gyrokinetic code GEM based on the EAST experimental parameters. The linear simulation results show that ECM is an electrostatic mode with dominant toroidal mode number n=18 and frequency about 48kHz, and propagates along the direction of electron diamagnetic drift, which are consistent with the experimental results. In addition, the density and electron temperature gradients destabilize the mode, while the collision stabilizes the mode. The nonlinear simulation results show that the saturated particle and heat fluxes induced by ECM are mainly due to the perturbed electrostatic ExB drift, and the fluxes of electrons and ions are almost equal. The ECM drives significant outward particle and heat fluxes, thus greatly promoting the maintenance of the long pulse H-mode. The Fourier decomposition of fluxes and potentials demonstrate that the intermediate-n modes of n=14, 18 grow fastest in the linear phase, while in the nonlinear saturation phase, the low-n modes such as n=4, 6 dominate and the fluxes are mainly contributed by the mode of n=10. It is found that zonal flow is not the dominant saturation mechanism of the turbulence. The inverse spectral cascade of turbulence is inevitably observed in the nonlinear saturation process, indicating that it is a more universal turbulence saturation mechanism. It is also found that radial electric field can greatly reduce the turbulence intensity and transport level. From the analyses of frequency and transport channels, it can be concluded that ECM appears to be the collisionless trapped electron mode (CTEM).

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Experimental observation of coexisting electromagnetic fluctuations correlating with the inter-ELM pedestal evolution on EAST

Cited by 11 publications

References 86 publications

Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

Global gyrokinetic simulation of edge coherent mode in EAST

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