Spatiotemporal Structures of Edge Limit-Cycle Oscillation before L-to-H Transition in the JFT-2M Tokamak

Kobayashi, Tatsuya; Itoh, K.; Ido, T.; Kamiya, K.; Itoh, Sanae I.; Miura, Y.; Nagashima, Yoshihiko; Fujisawa, A.; Inagaki, S.; Ida, K.; Hoshino, K.

doi:10.1103/physrevlett.111.035002

Cited by 104 publications

(142 citation statements)

References 25 publications

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“…Thus, the experimental argument based upon the orbit loss mechanism in Ref. 27 and the conventional Reynolds stress argument work together. In the present simulation of a fast bifurcation event, the Reynolds work causes a conservative eddy tilting-stretching-absorption process, with the orbit-loss then taking over with the shearing of eddies to smaller-scale dissipative eddies and finishing up the turbulence quenching process and keeping the turbulence suppressed.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…25,26 Some experiments (i.e., Ref. 27) report a different evidence that the experimentally observed Reynolds work is too weak to explain the L-H bifurcation and, thus, the E Â B shearing from the neoclassical orbit loss physics 28,29 is solely responsible for the bifurcation. Some LCO type transition experiments that showed little Reynolds work suggest that the E Â B shearing from the buildup of the steep pressure pedestal is responsible for the turbulence suppression.…”

Section: Introductionmentioning

confidence: 99%

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A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

et al. 2018

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Article:Ku, S., Chang, C. S., Hager, R. et al. (9 more authors) (2018) A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1. Physics of Plasmas. 056107. ISSN 1089-7674 https://doi.org/10.1063/1.5020792 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1 A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1 A fast edge turbulence suppression event has been simulated in the electrostatic version of the gyrokinetic particle-in-cell code XGC1 in a realistic diverted tokamak edge geometry under neutral particle recycling. The results show that the sequence of turbulent Reynolds stress followed by neoclassical ion orbit-loss driven together conspire to form the sustaining radial electric field shear and to quench turbulent transport just inside the last closed magnetic flux surface. The main suppression action is located in a thin radial layer around w N ' 0:96-0:98, where w N is the normalized poloidal flux, with the time scale $0:1ms.Published by AIP Publishing. https://doi

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Section: Conclusion and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

et al. 2018

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“…While some experiments 4,5,7,9 suggest that significant zonal flow growth by Reynolds work precedes, and in fact triggers, the L ! H transition, others 19,20 suggest that the mean E Â B flow evolution leads that of the zonal flow.…”

Section: Introductionmentioning

confidence: 99%

Flux-driven simulations of turbulence collapse

et al. 2015

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Using three-dimensional nonlinear simulations of tokamak turbulence, we show that an edge transport barrier (ETB) forms naturally once input power exceeds a threshold value. Profiles, turbulence-driven flows, and neoclassical coefficients are evolved self-consistently. A slow power ramp-up simulation shows that ETB transition is triggered by the turbulence-driven flows via an intermediate phase which involves coherent oscillation of turbulence intensity and E Â B flow shear. A novel observation of the evolution is that the turbulence collapses and the ETB transition begins when R T > 1 at t ¼ t R (R T : normalized Reynolds power), while the conventional transition criterion (x EÂB > c lin where x EÂB denotes mean flow shear) is satisfied only after t ¼ t C ( >t R ), when the mean flow shear grows due to positive feedback. V C 2015 AIP Publishing LLC.

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“…Limit-cycle oscillations (LCOs) preceding the transition from low (L-mode) to high confinement (H-mode) are intensively studied [1][2][3][4][5][6][7][8][9]. The regime dominated by LCOs is also called I-phase [1], dithering or transient mode.…”

mentioning

confidence: 99%

“…The turbulent generated flows appear as lowfrequency zonal flows [2][3][4][5][6][7][8][9]12] or geodesic acoustic oscillations [1]. Whereas the basic mechanism of turbulence suppression by zonal flows [13][14][15][16], the existence of zonal flows during the L-H transition [12] and the predatorprey dynamics in general [17] have been experimentally demonstrated, turbulence suppression by flow generation appears strong enough to trigger a transition into the Hmode [1,2,4,5,9,18] but some experiments show only weak or insufficient zonal flow activity at the L-H transition [6,7,19,20]. Recently also magnetic fluctuations are observed during these limit cycle oscillations [7,8,[20][21][22] even though the predator-prey model [10,11] is electrostatic in nature.…”

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confidence: 99%

Poloidal asymmetric flow and current relaxation of ballooned transport during I-phase in ASDEX Upgrade

et al. 2016

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Turbulence driven poloidal asymmetric parallel flow and current perturbations are studied for tokamak plasmas of circular geometry. Whereas zonal flows can lead to in-out asymmetry of parallel flows and currents via the Pfirsch-Schlüter mechanism, ballooned transport can result in an updown asymmetry due to the Stringer spin-up mechanism. Measurements of up-down asymmetric parallel current fluctuations occurring during the I-phase in ASDEX Upgrade are not responses to the equilibrium by the Pfirsch-Schlüter current, but can be interpreted as a response to strongly ballooned plasma transport coupled with the Stringer spin-up mechanism. A good agreement of the experimental measured limit-cycle frequencies during I-phase with the Stringer spin-up relaxation frequency is found.

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Spatiotemporal Structures of Edge Limit-Cycle Oscillation before L-to-H Transition in the JFT-2M Tokamak

Cited by 104 publications

References 25 publications

A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

Flux-driven simulations of turbulence collapse

Poloidal asymmetric flow and current relaxation of ballooned transport during I-phase in ASDEX Upgrade

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