Suppression of Transport Cross Phase by Strongly Sheared Flow

Terry, P. W.; Newman, D. E.; Ware, A. S.

doi:10.1103/physrevlett.87.185001

Cited by 63 publications

(79 citation statements)

References 19 publications

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“…A reduction of 30 % was observed in the phase of maximum ZF amplitude which was sustained beyond the lifetime of the ZF. In agreement with theory [34,35], it was shown that the turbulent transport reduction is initially induced by a modification of the cross phase between density and potential fluctuations and later maintained by reduced fluctuation amplitudes. The findings underline the importance of ZFs as a trigger for global confinement phenomena like the transition from L-to H-mode.…”

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confidence: 85%

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Experimental Evidence of Turbulent Transport Regulation by Zonal Flows

et al. 2013

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Abstract. The regulation of turbulent transport by zonal flows is studied experimentally on a flux surface of the stellarator experiment TJ-K. Data of 128 Langmuir probes at different toroidal and poloidal positions on a single flux surface enable to measure simultaneously the zonal flow activity and the turbulent transport in great detail. A reduction of turbulent transport by 30 % during the zonal flow phase is found. It is shown that the reduction process is initiated by a modification in the cross phase between density and electric field followed by a reduction in the fluctuation levels, which sustain low transport levels on larger time scales than the zonal flow life time.

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confidence: 85%

“…3 reaches zero. Thus, in the early phase of the ZF the cross phase α nE rather than the turbulent amplitudes is relevant for transport reduction as it was already emphasized in theoretical [34,35] works. Also biasing experiments indicated that shear flows mainly act on the cross phase [36,37,25].…”

mentioning

confidence: 78%

Experimental Evidence of Turbulent Transport Regulation by Zonal Flows

et al. 2013

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“…Models based on radial decorrelation of turbulent structures by sheared flow are prevalent in the theoretical literature [16][17][18][19][20][21][22][23][24][25] and provide a number of predictions concerning the quantitative scaling of turbulent quantities with shear. The basic premise underlying these models is the competition between linear or nonlinear turbulence dynamics and the tendency of sheared flows to "rip apart" or decorrelate turbulent structures; this leads to reduced fluctuation amplitude and decreased radial transport step-size.…”

Section: Introductionmentioning

confidence: 99%

Turbulence and transport suppression scaling with flow shear on the Large Plasma Device

et al. 2013

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Continuous control over azimuthal flow and shear in the edge of the Large Plasma Device (LAPD) [W. Gekelman et al., Rev. Sci. Instr. 62, 2875(1991] has been achieved using a biasable limiter. This flow control has allowed a careful study of the effect of flow shear on pressure-gradient-driven turbulence and particle transport in LAPD. The combination of externally controllable shear in a turbulent plasma along with the detailed spatial diagnostic capabilities on LAPD makes the experiment a useful testbed for validation of shear suppression models. Motivated by these models, power-law fits are made to the density and radial velocity fluctuation amplitudes, particle flux, density-potential crossphase, and radial correlation length. The data show a break in the trend of these quantities when the shearing rate (c s ¼ @V h =@r) is comparable to the turbulent decorrelation rate (1=s ac ). No one model captures the trends in the all turbulent quantities for all values of the shearing rate, but some models successfully match the trend in either the weak (c s s ac < 1) or strong (c s s ac > 1) shear limits. V C 2013 AIP Publishing LLC. [http://dx

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“…This flux can be decreased due to either a reduction in the amplitude of any of the fluctuating fields 4 or to an appropriate shift in the phase between advected and advecting fields. 12 The details of how this suppression happens are however often complicated and still not well understood in many cases. Mostly for that reason, the investigation of these various possibilities in a tokamak geometry is traditionally done by assuming ab initio that some effective diffusivity can be used to characterize radial transport in the absence of any poloidal ͑and toroidal͒ flow.…”

Section: Introductionmentioning

confidence: 99%

On the nature of radial transport across sheared zonal flows in electrostatic ion-temperature-gradient gyrokinetic tokamak plasma turbulence

Sánchez¹,

Newman²,

Leboeuf³

et al. 2009

Physics of Plasmas

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It is argued that the usual understanding of the suppression of radial turbulent transport across a sheared zonal flow based on a reduction in effective transport coefficients is, by itself, incomplete. By means of toroidal gyrokinetic simulations of electrostatic, ion-temperature-gradient turbulence, it is found instead that the character of the radial transport is altered fundamentally by the presence of a sheared zonal flow, changing from diffusive to anticorrelated and subdiffusive. Furthermore, if the flows are self-consistently driven by the turbulence via the Reynolds stresses ͑in contrast to being induced externally͒, radial transport becomes non-Gaussian as well. These results warrant a reevaluation of the traditional description of radial transport across sheared flows in tokamaks via effective transport coefficients, suggesting that such description is oversimplified and poorly captures the underlying dynamics, which may in turn compromise its predictive capabilities.

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Suppression of Transport Cross Phase by Strongly Sheared Flow

Cited by 63 publications

References 19 publications

Experimental Evidence of Turbulent Transport Regulation by Zonal Flows

Experimental Evidence of Turbulent Transport Regulation by Zonal Flows

Turbulence and transport suppression scaling with flow shear on the Large Plasma Device

On the nature of radial transport across sheared zonal flows in electrostatic ion-temperature-gradient gyrokinetic tokamak plasma turbulence

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