Role of Zonal Flow Predator-Prey Oscillations in Triggering the Transition to H-Mode Confinement

Schmitz, L.; Zeng, L.; Rhodes, T. L.; Hillesheim, J.C.; Doyle, E. J.; Groebner, R. J.; Peebles, W. A.; Burrell, K.H.; Wang, G.

doi:10.1103/physrevlett.108.155002

Cited by 261 publications

(311 citation statements)

References 19 publications

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“…These oscillations have in fact been experimentally demonstrated close to the H-mode threshold. [30] The second step to a sustained H-mode, i.e. a permanent suppression of turbulence, is therefore a growth of the edge pressure gradient (a second predator) during the phase when turbulence is reduced by the zonal flow.…”

Section: Discussionmentioning

confidence: 99%

Zonal flow production in the L–H transition in Alcator C-Mod

Cziegler¹,

Tynan²,

Diamond³

et al. 2014

Plasma Phys. Control. Fusion

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Abstract. Transitions of tokamak confinement regimes from low-to highconfinement are studied on Alcator C-Mod [1] tokamak using gas-puff-imaging (GPI) with a focus on the interaction between the edge drift-turbulence and the local shear flow. Results show that the nonlinear turbulent kinetic energy transfer rate into the shear flow becomes comparable to the estimated value of the drift turbulence growth rate at the time the turbulent kinetic energy starts to drop, leading to a net energy transfer that is comparable to the observed turbulence losses. A corresponding growth is observed in the shear flow kinetic energy. The above behavior is demonstrated across a series of experiments. Thus both the drive of the edge zonal flow and the initial reduction of turbulence fluctuation power are shown to be consistent with a lossless kinetic energy conversion mechanism, which consequently mediates the transition into H-mode. The edge pressure gradient is then observed to build on a slower (1ms) timescale, locking in the H-mode state. These results unambiguously establish the time sequence of the transition as: first the peaking of the normalized Reynolds power, then the collapse of the turbulence, and finally the rise of the diamagnetic electric field shear as the L-H transition occurs.

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Section: Discussionmentioning

confidence: 99%

Zonal flow production in the L–H transition in Alcator C-Mod

Cziegler¹,

Tynan²,

Diamond³

et al. 2014

Plasma Phys. Control. Fusion

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“…In this article blob refers to a coherent structure with high density with respect to the surrounding fluctuation level. It is widely accepted that poloidal shear flows increase the particle and energy confinement in fusion devices [2][3][4][5][6]. Recently, the extraordinary role of shear layers for blob generation has been identified [7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Turbulent transport across shear layers in magnetically confined plasmas

et al. 2014

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Shear layers modify the turbulence in diverse ways and do not only suppress it. A spatialtemporal investigation of gyrofluid simulations in comparison with experiments allows to identify further details of the transport process across shear layers. Blobs in and outside a shear layer merge, thereby exchange particles and heat and subsequently break up. Via this mechanism particles and heat are transported radially across shear layers. Turbulence spreading is the immanent mechanism behind this process.

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“…The organization of zonal flows, known as azimuthally symmetric band-like sheared flows, is a particularly challenging phenomenon for the understanding of dynamo effects, atmospherics jets, or transport regulation in magnetized plasmas 1 . The L-H confinement transition observed at the edge of tokamak plasmas is probably related to the turbulent drive of a sheared zonal flow associated with a strong inward gradient of electric field [2][3][4] .…”

Section: Introductionmentioning

confidence: 99%

On physical interpretation of two dimensional time-correlations regarding time delay velocities and eddy shaping

et al. 2012

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Time delay estimation (TDE) techniques are frequently used to estimate the flow velocity from fluctuating measurements. Tilted structures carried by the flow lead to misinterpretation of the time delays in terms of velocity direction and amplitude. It affects TDE measurements from probes, and is also intrinsically important for beam emission spectroscopy (BES) and gas puff imaging (GPI) measurements. Local eddy shapes estimated from 2D fluctuating field are necessary to gain a more accurate flow estimate from TDE, as illustrated by Langmuir probe array measurements. A least square regression approach is proposed to estimate both flow field and shaping parameters. The technique is applied to a test case built from numerical simulation of interchange fluctuations. The local eddy shape does not only provide corrections for the velocity field, but also quantitative informations about the statistical interaction mechanisms between local eddies and E × B flow shear. The technique is then tested on gaz puff imaging data collected at the edge of EAST tokamak plasmas. It is shown that poloidal asymmetries of the fluctuation fields -velocity and eddy shape -are consistent at least qualtitatively with a ballooning type of turbulence immersed in a radially sheared equilibrium flow.

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Role of Zonal Flow Predator-Prey Oscillations in Triggering the Transition to H-Mode Confinement

Cited by 261 publications

References 19 publications

Zonal flow production in the L–H transition in Alcator C-Mod

Zonal flow production in the L–H transition in Alcator C-Mod

Turbulent transport across shear layers in magnetically confined plasmas

On physical interpretation of two dimensional time-correlations regarding time delay velocities and eddy shaping

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