Fluctuation-Induced Energy Flux in the Tokamak Edge

Ritz, Ch. P.; Bravenec, R. V.; Schoch, P. M.; Bengtson, Roger D.; Boedo, J. A.; Forster, John; Gentle, K. W.; He, Ying; Hickok, R. L.; Kim, Y. J.; Lin, Hong; Phillips, P. E.; Rhodes, T. L.; Rowan, W. L.; Valanju, P.; Wootton, A. J.

doi:10.1103/physrevlett.62.1844

Cited by 167 publications

(77 citation statements)

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“…The calculated flux, shown in Fig. 3(a), is an upper limit for sheared plasmas and accurate for the OH conditions since a strong T e -Ẽ u correlation has been documented for nonsheared plasmas in a variety of tokamaks [13,14]. Even the upper limit shows a factor of 4 reduction in the conducted heat flux for strong E 3 B shear [ Fig.…”

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confidence: 99%

“…The total powerP e T carried across the LCFS by the sum of turbulent electron convectionP e conv and conductionP e cond , if assumed uniform over the cross section, can account for ϳ60% and ϳ18% of the total in OH and H plasmas, respectively. If an equal ion contribution is assumed and added [13], thenP i1e T ϳ 120% ͑OH͒ and ϳ36% ͑H͒ of the total power. Therefore, anomalous transport accounts for the power balance in OH, but not in H, conditions.…”

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Suppression of Temperature Fluctuations and Energy Barrier Generation by Velocity Shear

Boedo

Gray

et al. 2000

Phys. Rev. Lett.

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First measurements of temperature fluctuations in a region of high velocity shear show that absolute and normalized fluctuation levels are reduced across the shear layer, a result that is consistent with weak parallel electron thermal conduction in the electron temperature dynamics. The concomitant reduction of temperature, density, and electric field fluctuations reduces the anomalous conducted and convected heat fluxes.PACS numbers: 52.35. Ra, 52.25.Gj, 52.55.Fa The presence of localized flow shear in fluids, in general, and plasmas, in particular, can reduce turbulence levels and cross-flow transport, creating a transport barrier. Such barriers develop spontaneously in a wide variety of magnetically confined plasmas, producing transitions from a low energy confinement state (L mode) to a higher energy confinement state (H mode) [1]. The L-H transition in magnetically confined plasmas is accompanied by a reduction of turbulence levels [2], confirming the paradigm that microturbulence is responsible for a considerable part of the energy and particle losses [3]. Behavior similar to that of the spontaneous L-H transition is obtained by applying an external radial electric field to the plasma using an electrode [4], indicating that the radial electric field and resulting E 3 B rotation play a crucial role. The shearing of turbulent eddies by differential rotation has been proposed as a universal mechanism to stabilize turbulence in plasmas [5] ( E 3 B generated), but it is also postulated to operate in nonionized fluids, such as two-dimensional Navier-Stokes turbulence and the stratosphere [6]. Electrode bias experiments have clarified the role of the radial electric field and its bifurcation [7] in L-H transitions by correlating the externally applied electric fields with the reduction in turbulence levels [8], formation of a transport barrier, and resulting confinement improvement. The E 3 B velocity shear in plasmas can affect nonlinearly saturated turbulence and reduce transport by acting on both the amplitude of the fluctuations and the phase between the density and potential fluctuations [9]. The shearing rate, v E3 B , must be comparable to Dv D , the nonlinear turbulence decorrelation rate in the absence of shear. Turbulence suppression is achieved in nonlinear simulations when the rate v E3 B ͑v E3 B dV E3 B ͞dr͒ is of the order of the linear growth rate v ins of the dominant mode in the plasma [10]. Turbulent decorrelation theory [9] predicts suppression of arbitrary advected fluctuations, including temperature, under E 3 B shearing. Predictions are consistent with observations of reductions in density and potential fluctuations [10] in particle transport barriers, but no direct measurements exist quantifying temperature fluctuations in a transport barrier. We report those measurements in this paper and examine the associated heat fluxes in light of recent theoretical work [9] that has indicated that if parallel thermal conduction is strong, flow shear can reduce the particle flux, but have little eff...

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Suppression of Temperature Fluctuations and Energy Barrier Generation by Velocity Shear

Boedo

Gray

et al. 2000

Phys. Rev. Lett.

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“…doi:10.1016/j.jcp.2009.09.031 existence of large scale flows generated by both the magnetic equilibrium and the plasma turbulence are also observed to play an important role in this interface region [2]. Other experimental [3,4] and theoretical studies [5,6] suggest that turbulence and transport properties are dramatically different in the core and in the SOL. The physics taking place at the interface between these two layers, ie in the vicinity of the Last Closed FLux Surface (LCFS), is still under investigation.…”

Section: Introductionmentioning

confidence: 87%

TOKAM-3D: A 3D fluid code for transport and turbulence in the edge plasma of Tokamaks

Tamain

Ghendrih

Tsitrone

et al. 2010

Journal of Computational Physics

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“…For the LOC regime, the sign þ is used in (1) as both the E Â B rotation, and the turbulence propagate in the electron diamagnetic direction. For the SOC regime, the turbulence propagates opposite in the ion diamagnetic direction, imposing then the use of sign À in (1). The E Â B rotation velocity V EÂB in (1) was deduced from the radial electric field, which can be estimated by the thermal ripple losses in case of a strong ripple such as in Tore Supra.…”

Section: Synthetic Reflectometry Simulations a Full-wave Computmentioning

confidence: 99%

Simulation of core turbulence measurement in Tore Supra ohmic regimes

Hacquin¹,

Citrin²,

Arnichand³

et al. 2016

Physics of Plasmas

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This paper reports on a simulation of reflectometry measurement in Tore Supra ohmic discharges, for which the experimental observations as well as gyrokinetic non-linear computations predict a modification of turbulence spectrum between the linear (LOC) and the saturated ohmic confinement (SOC) regimes. Synthetic reflectometry simulations coupling full-wave computations with gyrokinetic data are carried out. This allows a direct comparison between the gyrokinetic non-linear predictions and experimental observations. The synthetic diagnostic results are found in a good agreement with the experimental findings; in particular, they reproduce well the quasi-coherent peak in the fluctuation spectrum of LOC regimes dominated by a trapped electron mode turbulence. It is also shown that such synthetic tools are valuable for (i) an enhanced interpretation of the reflectometry measurement (for instance, through the investigation of the 2D effects) and (ii) a better understanding of the turbulence properties (for instance, via the analysis of its poloidal asymmetry).

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Fluctuation-Induced Energy Flux in the Tokamak Edge

Cited by 167 publications

References 23 publications

Suppression of Temperature Fluctuations and Energy Barrier Generation by Velocity Shear

Suppression of Temperature Fluctuations and Energy Barrier Generation by Velocity Shear

TOKAM-3D: A 3D fluid code for transport and turbulence in the edge plasma of Tokamaks

Simulation of core turbulence measurement in Tore Supra ohmic regimes

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