Pedestal dynamics prior to type-III ELM onset on HL-2A tokamak*

Cheng, J.; Dong, J. Q.; Itoh, K.; Itoh, Sanae–I.; Yan, L.W.; He, Yanfang; Li, Wei; Zhou, Hai; Xu, Jianqiang; Huang, Z.H.; Wu, Na; Zhao, K.J.; Shi, Z.B.; Kosuga, Y.; Sasaki, M.; Han, Mingkun; Wang, Jialei; Liu, Yi; Xu, M.; Xu, Yuhong

doi:10.1088/1741-4326/ab9884

Cited by 8 publications

(6 citation statements)

References 30 publications

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“…The impurity experiments were performed in ohmicallyheated deuterium plasmas on the HL-2A tokamak (a/R = 0.4 m/1.65 m) with the limiter configuration under the following discharge parameters: plasma current I p ≈ 190 kA, line-averaged density n el ≈ 2 × 10 19 m −3 , toroidal magnetic field B t ≈ 1.5 T, edge safety factor q ∼ 3.6 and edge ion-ion collisionality v ii ≈ 3-5 kHz. Recently, zonal flow [16], the energy transfer rate [17], limit-cycle oscillations [18][19][20], pedestal instability [21] and the divertor particle flux [22] have been actively studied in the HL-2A tokamak with multiple Langmuir probe arrays [23]. Figure 1(a) depicts the arrangement of the stationary Langmuir probe at point A and the reciprocating system at point B, both located at the outer mid-plane in the HL-2A tokamak.…”

Section: Methodsmentioning

confidence: 99%

Effect of impurity ions on the coupling between zonal flow and local turbulent transport in HL-2A plasmas

Zou¹,

Cheng²,

Xu³

et al. 2022

Nucl. Fusion

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The effect of impurity ions on the coupling between geodesic acoustic mode (GAM) zonal flows and local turbulent transport has been studied using a Langmuir probe array in HL-2A ohmically-heated deuterium plasmas. The experimental results illustrate that both frequency and amplitude level of the GAM zonal flow significantly reduce with the increase of carbon ions concentration, which is qualitatively consistent with the theoretical prediction [B. Xie et al. Plasma Phys. Controlled Fusion 60 025015 (2018)], meanwhile the less energy is transferred from turbulence to GAM zonal flows due to the reduction in tilting and stretching of turbulent vortex. Consequently, the impurity ions stir the enhancement of turbulence and turbulent transport owing to the reduced GAM zonal flow as demonstrated in the experiment. These experimental results presented here therefore reveal the dual roles played by impurity ions on the dynamics of GAM zonal flows.

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Section: Methodsmentioning

confidence: 99%

Effect of impurity ions on the coupling between zonal flow and local turbulent transport in HL-2A plasmas

Zou¹,

Cheng²,

Xu³

et al. 2022

Nucl. Fusion

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“…For example, the Type-III ELM regime has traditionally been associated with the resistive-ballooning mode. Recently, experimental analysis on the HL-IIA tokamak [44][45] has demonstrated that streamers develop in the plasma core during the internal energy collapse phase, corresponding to the onset of Type-III ELMs. These results are consistent with large-scale nonlinear simulations indicating the existence of unexpected and distinct physical mechanisms for Type-III ELMs.…”

Section: Comparison With Previous Workmentioning

confidence: 99%

Unveiling the Trigger Mechanism of an Explosive Plasma Eruption in a Toroidal Magnetic Fusion Device

Kamiya

Itoh

Matsunaga

et al. 2023

Preprint

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Explosive phenomena, such as edge-localized modes (ELMs) in controlled-nuclear-fusion-devices and solar flares on the sun, have eluded scientists for a long time. Despite extensive investigation in laboratory and astrophysical plasmas, the trigger mechanism has remained elusive. Herein, we present the dynamics of tearing parity mode during an explosive eruption in magnetized plasmas and identified a critical threshold for mode amplitude. When the amplitude exceeds this threshold, an ELM-event is triggered, inducing the collapse of the plasma. The result also demonstrates rapid magnetic reconnection and the formation of stochasticity in magnetic field lines. The observed timescale between trigger events and the subsequent large-scale collapse provides a semiquantitative support for the hypothesis that magnetic braiding causes nonlinear instability and explosive growth. As a corollary, the mechanism of ELM-control using external magnetic-coils is also elucidated. These results have significant implications for laboratory and astrophysical understanding of magnetized plasma dynamics.

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“…The bispectral analysis technique [33] has been widely used to study the nonlinear coupling in several experiments [34][35][36]. The squared auto-bicoherence is defined as b It is clearly shown that the bicoherence values along the f 2 = ±11.7 kHz and f 2 = − f 1 ± 11.7 kHz lines in the case with tungsten ions are much larger than those without tungsten injection, indicating that the nonlinear coupling of fluctuations is significantly enhanced with tungsten injection.…”

Section: Evidence For the Enhanced Interaction Of Gam And Turbulencementioning

confidence: 99%

Observation of reduced-turbulence regime with tungsten injection in HL-2A edge plasmas

Zou,

Cheng,

Shi

et al. 2023

Nucl. Fusion

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A reduced-turbulence regime has been observed in HL-2A NBI-heated deuterium plasmas. The transition to this regime was achieved by injecting certain amount of tungsten into plasma based on the laser blow-off (LBO) technique. It has been found that the amplitude of geodesic acoustic mode (GAM) zonal flow, turbulent vortex sizes together with eddy tilting angle are all significantly increased in the edge region after the tungsten injection, but the frequency of GAM zonal flow keeps nearly unchanged. Measurement shows the nonlinear coupling degree of turbulence dramatically increases, meanwhile the collisional damping of GAM zonal flow has slight drop, concluding that the increased nonlinear coupling is the main cause for the excitation of GAM zonal flow, which consequently results in the reduction of turbulent transport as observed in this experiment. These results given here indicate that the tungsten ions play an active role in turbulence-GAM dynamics through symmetry-breaking mechanism, which could help us to better understand the inherent physical mechanism governing turbulent transport in the presence of high-Z impurity ions in fusion plasmas.

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Pedestal dynamics prior to type-III ELM onset on HL-2A tokamak*

Cited by 8 publications

References 30 publications

Effect of impurity ions on the coupling between zonal flow and local turbulent transport in HL-2A plasmas

Effect of impurity ions on the coupling between zonal flow and local turbulent transport in HL-2A plasmas

Unveiling the Trigger Mechanism of an Explosive Plasma Eruption in a Toroidal Magnetic Fusion Device

Observation of reduced-turbulence regime with tungsten injection in HL-2A edge plasmas

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