First Evidence of Local 
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 Drift in the Divertor Influencing the Structure and Stability of Confined Plasma near the Edge of Fusion Devices

Wang, H. Q.; Guo, H.Y.; Xu, G. S.; Leonard, A.W.; Wu, Xiaoxiao; Groth, M.; Jaervinen, A.E.; Watkins, J. G.; Osborne, T.H.; Thomas, D. M.; Eldon, D.; Stangeby, P.C.; Turco, F.; Xu, Jichan; Wang, L.; Wang, Y. F.; Liu, J. B.

doi:10.1103/physrevlett.124.195002

Cited by 24 publications

(41 citation statements)

References 36 publications

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“…A density shelf structure has been observed to reside in the near-SOL region in both regimes in figure 4(a). Previous studies have reported that the density shelf structure is correlated with a doubly peaked density profile near the divertor target plate, which tends to occur for operation with the ion B × ∇B drift direction away from the X-point, as employed for DIII-D advanced tokamak scenarios [39]. In addition, a relatively closed divertor configuration [40] is also thought to be beneficial for the achievement of the high SOL density.…”

Section: Typical Pedestal Profilesmentioning

confidence: 99%

“…The plasma density at the separatrix is so high that the recycling neutrals are ionized mostly in the SOL and divertor regions, and the penetration into the pedestal is weak. Combined with the strong particle exhaust across the pedestal driven by the edge localized instabilities as well as the neoclassical transport, the flat density pedestal with high SOL density is expected, which potentially allows the access to the grassy ELM regime much easier [39]. The grassy ELM regime has been chosen as the primary ELM solution for CFETR [3,4].…”

Section: Electron Density N E Profile Simulation and Pedestal Stabili...mentioning

confidence: 99%

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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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Section: Typical Pedestal Profilesmentioning

confidence: 99%

Section: Electron Density N E Profile Simulation and Pedestal Stabili...mentioning

confidence: 99%

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

Wang

et al. 2020

Nucl. Fusion

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“…9 Such profiles with double peak structure have been observed in many machines. 3,[10][11][12][13] In this paper, we will highlight that the double peak structure is mainly due to the important transport effects taking place in the divertor.…”

Section: Introductionmentioning

confidence: 97%

“…In turn, divertor plasma conditions could significantly affect the upstream-downstream relationship. 3 Besides the upstream-downstream relationship, several other mechanisms are considered to influence the divertor plasma heat and Phys. Plasmas 28, 052509 (2021); doi: 10.1063/5.0048609…”

Section: Introductionmentioning

confidence: 99%

Effects of divertor electrical drifts on particle distribution and detachment near the divertor target plate in DIII-D

et al. 2021

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Strong impacts of drifts on the divertor plasma in-out asymmetry and detachment are demonstrated in DIII-D with an open divertor configuration. For forward toroidal field, B T , i.e., with the ion B Â rB drift toward the divertor, the particle flux to the inner divertor, as represented by the Langmuir probe measured ion saturation current (J sat ), exhibits a double peak structure, with electron temperature, lower at the inner target. Reversing the B T direction reverses both the radial and poloidal E Â B flows, leading to a broad particle flux profile in the outboard scrape-off layer (SOL) with a similar double-peak structure to that observed at the inner target with forward B T . The correlation of a double peak structure with divertor temperature profiles confirms physical coupling between the drift flow and sheath boundary condition and their strong impact on divertor profiles. In addition, under reversed B T conditions, increasing the density flattens the target temperature profile. However, J sat remains high away from the strike point, rendering it difficult to achieve an "effective" detached plasma, i.e., with effective reduction in both peak heat flux and peak temperature (in the far SOL). In contrast, divertor detachment with a cold and flat temperature profile can be achieved at both target plates with the forward B T .

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“…The electric field perpendicular to magnetic field lines is a particularly important quantity as it is a strong drive of cross-field fluxes and thus edge pressure profiles on turbulent scales. These E × B flows are observed to strongly influence edge plasma stability [219,230] and the motion of coherent structures which can account for significant particle losses during standard operation of tokamaks [40,21,111]. Resultant turbulence-induced fluxes impacting walls can cause sputtering, erosion, and impurity injection which can further adversely affect safe operation and confinement of fusion plasmas [40,108,109].…”

Section: Magnetic Confinement Fusionmentioning

confidence: 99%

Physics-informed machine learning techniques for edge plasma turbulence modelling in computational theory and experiment

Mathews¹

2022

Preprint

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First Evidence of Local E×B Drift in the Divertor Influencing the Structure and Stability of Confined Plasma near the Edge of Fusion Devices

Abstract: This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail.

Cited by 24 publications

References 36 publications

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

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

Effects of divertor electrical drifts on particle distribution and detachment near the divertor target plate in DIII-D

Physics-informed machine learning techniques for edge plasma turbulence modelling in computational theory and experiment

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