A Dip Structure in the Intrinsic Toroidal Rotation Near the Edge of the Ohmic Plasmas in EAST

Xu, G. S.; Wan, Baonian; Guo, H.Y.; Zhang, Wei; Chang, Jiafeng; Niu, Y.; Ding, Siye; Zhang, Ling; Wang, Liang; Liu, Shaocheng; Liu, Peng; Jiang, M.; Wang, Huiqian; Xiao, C.; Gao, Xiang; Hu, Liqun; Zhu, Shengyu; Wu, Zhenwei; Qian, J.; Gong, Xianzu

doi:10.1088/1009-0630/13/4/03

Cited by 12 publications

(10 citation statements)

References 38 publications

(50 reference statements)

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“…Therefore, the generation process of flows directly provides a suppression mechanism of turbulence, leading to a net decay of turbulence energy. The estimated energy transfer rate W ⊥ /| ṽr | 2 ∼ 1 × 10 6 s −1 is significantly higher than the typical collisional damping rate of flows (∼2 × 10 4 s −1 ) or the turbulence decorrelation rate (∼1 × 10 5 s −1 ) at the plasma edge, measured by reciprocating probes in EAST [13,19,74].…”

Section: Experimental Results From Gpi Measurementsmentioning

confidence: 69%

“…Furthermore, the energy gain by the global flows at the plasma edge in one dithering cycle is estimated to be 0.5m i ε ⊥ v p 2 ∼ 10 eV/ion [13,19,74], which is of the same order as the turbulence energy loss during the suppression, e| φ| + 0.5m i | ṽ⊥ | 2 ∼ 10 eV/ion, where | φ| ∼ 10 V is the plasma electrostatic potential fluctuation level, and the kinetic energy of the E ×B flow fluctuation, 0.5m i | ṽ⊥ | 2 , is small with respect to e| φ|. Therefore, the energy transfer from turbulence to flows is sufficiently strong to account for the observed flow generation during the I-phase.…”

Section: Experimental Results From Gpi Measurementsmentioning

confidence: 99%

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Study of the L–I–H transition with a new dual gas puff imaging system in the EAST superconducting tokamak

Shao

Liu

et al. 2013

Nucl. Fusion

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Abstract:The intermediate oscillatory phase during the L-H transition, termed I-phase, has been studied in the EAST superconducting tokamak by employing a newly developed dual gas puff imaging (GPI) system near the L-H transition power threshold. The experimental observations suggest that the oscillatory behavior appearing at the L-H transition could be induced by the synergistic effect of the two components of the sheared m,n=0 E´B flow, i.e., the turbulence-driven zonal flow (ZF) and the equilibrium flow (EF). The latter arises from the neoclassical equilibrium, and is, to leading order, balanced by the ion diamagnetic term in the radial force balance equation. A slow increase in the poloidal flow and its shear at the plasma edge are observed tens of milliseconds prior to the I-phase. During the I-phase, the turbulence level decays and recovers periodically. The turbulence recovery appears to originate from the vicinity of the separatrix with clear wave fronts propagating both outward into the far scrape-off layer and inward into the core plasma. The Reynolds work done by the turbulence on the ZFs has been directly measured using the GPI system in the experiments, providing a direct evidence of kinetic energy transfer from turbulence to ZFs, thus driving the ZFs at the plasma edge. The ZFs are damped shortly after turbulence suppression, due to the 2 loss of turbulent drive, which then leads to the subsequent recovery of the turbulence level, initiating the next dithering cycle, or followed by a final transition into the H-mode, as the EF shear is strong enough to maintain turbulence suppression, even without the assistance of the ZF shear. A new self-consistent zero-dimensional model, incorporating the evolution of the EF and ZF shear, as well as the parallel transport in the scrap-off layer, has been developed and successfully reproduced the L-I-H transition process with many features comparing favorably with the experimental observations.

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Section: Experimental Results From Gpi Measurementsmentioning

confidence: 69%

Section: Experimental Results From Gpi Measurementsmentioning

confidence: 99%

Study of the L–I–H transition with a new dual gas puff imaging system in the EAST superconducting tokamak

Shao

Liu

et al. 2013

Nucl. Fusion

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“…It exceeds 1×10 4 s −1 in the last few ms before the L-H transition. The rate is of the same order of the typical collisional damping rate of the poloidal flows, ∼1 × 10 4 s −1 , at the plasma edge [32,37,57]. In addition, we have estimated the time rate for the poloidal flow acceleration at the L-H transition, 1 2 1 + 2q 2 95 ∂ t V 2 E / δv 2 ⊥ ∼ 1 × 10 4 s −1 , where the poloidal flow inertia is enhanced by a factor, 1 + 2q 2 95 ∼ 30 [40], due to the well-known toroidal effect [5].…”

Section: Single-step L-h Transitionmentioning

confidence: 76%

Dynamics of L–H transition and I-phase in EAST

Wang

et al. 2014

Nucl. Fusion

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The turbulence and flows at the plasma edge during the L–I–H, L–I–L and single-step L–H transitions have been measured directly using two reciprocating Langmuir probe systems at the outer midplane with several newly designed probe arrays in the EAST superconducting tokamak. The E × B velocity, turbulence level and turbulent Reynolds stress at ∼1 cm inside the separatrix ramp-up in the last ∼20 ms preceding the single-step L–H transition, but remain nearly constant near the separatrix, indicating an increase in the radial gradients at the plasma edge. The kinetic energy transfer rate from the edge turbulence to the E × B flows is significantly enhanced only in the last ∼10 ms and peaks just prior to the L–H transition. The E × B velocity measured inside the separatrix, which is typically in the electron diamagnetic drift direction in the L-mode, decays towards the ion diamagnetic drift direction in response to fluctuation suppression at the onset of the single-step L–H, L–I–L as well as L–I–H transitions. One important distinction between the L–I–H and the L–I–L transitions has been observed, with respect to the evolution of the edge pressure gradient and mean E × B flow during the I-phase. Both of them ramp up gradually during the L–I–H transition, but change little during the L–I–L transition, which may indicate that a gradual buildup of the edge pedestal and mean E × B flow during the I-phase leads to the final transition into the H-mode. In addition, the transition data in EAST strongly suggest that the divertor pumping capability is an important ingredient in determining the transition behaviour and power threshold.

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“…38 In EAST, the SOL parallel flow has been analyzed, suggests a critical role of the Pfirsch-Schl€ uter (PS) flow as one of the most flowdriving mechanisms. [39][40][41][42] However, previous results are mainly achieved under the carbon wall divertor.…”

Section: -6mentioning

confidence: 99%

“…Still, it is not clear why the SOL flow is not reversed with reversing field direction, which is different from previous results on EAST under all carbon divertors. [39][40][41][42] This may be related to the up-down asymmetry divertors, in both material and geometry. In this paper, the role of neutral particle density on the L-H transition is qualitatively analyzed using the normalized divertor Da emission, however, diagnostics for the local T e , n e profile in the divertor region are needed.…”

Section: -10mentioning

confidence: 99%

Effect of ∇B drift on the H-mode power threshold in upper single null plasmas with ITER-like tungsten divertor on EAST

Chen

Niu

et al. 2018

Physics of Plasmas

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A Dip Structure in the Intrinsic Toroidal Rotation Near the Edge of the Ohmic Plasmas in EAST

Cited by 12 publications

References 38 publications

Study of the L–I–H transition with a new dual gas puff imaging system in the EAST superconducting tokamak

Study of the L–I–H transition with a new dual gas puff imaging system in the EAST superconducting tokamak

Dynamics of L–H transition and I-phase in EAST

Effect of ∇B drift on the H-mode power threshold in upper single null plasmas with ITER-like tungsten divertor on EAST

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