Effect of poloidal velocity shear on the edge fluctuations in the SINP tokamak

Saha, S. K.; Kumar, Rohit

doi:10.1088/0741-3335/46/7/006

Cited by 7 publications

(2 citation statements)

References 38 publications

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“…It was found in our experiment that coherent structures broke up partly in this area. Such a spatial decorrelation may be attributed to the strong shear of E × B flow around the limiter radius as reported earlier [32] . The decorrelation efficiency of the E × B flow can be quantified by calculating the shearing time τ shear ≡ λ ⊥ /(L r ∂ r V θ ), where τ shear is shear decorrelation time, λ ⊥ is structure poloidal size or wavelength, L r is the radial width of shear layer, ∂ r V θ is radial shear of perpendicular velocity.…”

Section: Blob Size and Velocity Scalingsupporting

confidence: 74%

Intermittent Bursts in the Boundary Plasma of HT-7

Niu¹,

Xu²,

Zhang³

et al. 2010

Plasma Sci. Technol.

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Intermittent characteristics of turbulence induced by coherent structures (blobs) was clearly observed in the ion saturation current signal, density fluctuation, particle flux and heat flux in HT-7. It is obvious that ion saturation current signal has deviated from Gaussian distribution and the skewness (S ) and flatness (K ) of signal increase radially outwards in the scrape-off layer (SOL). Using conditional analysis (CA), asymmetric character of the intermittent bursts are demonstrated. Owing to the radial propagation of the coherent structures, the particle density profile in SOL is non-exponential and flat outwards from the last close flux surface (LCFS). It is found around LCFS that the large burst fluctuations (above 2.5 rms) are responsible for about 50% of the total particle transport. Burst events move radially outwards with E θ ×B velocity, and the blob size can be calculated as δr ∼ Vrτc. Our experiment shows that the blob size, life time and drift velocity experienced a pronounced decorrelation in the shear layer. The electrostatic Reynolds stress components become very strong and show a radially steep gradient in the proximity of the shear layer. These experimental findings may imply that the coherent structures are titled by the developed shear flow in the E × B shear layer.

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Section: Blob Size and Velocity Scalingsupporting

confidence: 74%

Intermittent Bursts in the Boundary Plasma of HT-7

Niu¹,

Xu²,

Zhang³

et al. 2010

Plasma Sci. Technol.

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“…However, some debate still exists about the mechanism of transport reduction induced by mean flow shear, the focus being on the specific contributions from the suppression of fluctuation intensities and the relative phase between fluctuating quantities. In experiments, turbulent transport reductions resulting from the shearing effect of mean flows, which were either externally induced by biased electrodes or arose during the spontaneous L-H transition, were commonly observed in a variety of devices, [10][11][12][13][14][15][16][17][18][19][20][21] whereas discrepant mechanisms of transport suppressions were present among various plasma devices.…”

Section: Introductionmentioning

confidence: 99%

Observation of fluctuation-driven particle flux reduction by low-frequency zonal flow in a linear magnetized plasma

et al. 2015

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Low-frequency zonal flow (ZF) has been observed in a linear magnetic plasma device, exhibiting significant intermittency. Using the conditional analysis method, a time-averaged fluctuationinduced particle flux was observed to consistently decrease as ZF increased in amplitude. A dominant fraction of the flux, which is driven by drift-wave harmonics, is reversely modulated by ZF in the time domain. Spectra of the flux, together with each of the related turbulence properties, are estimated subject to two conditions, i.e., when potential fluctuation series represents a strong ZF intermittency or a very weak ZF component. Comparison of frequency-domain results demonstrates that ZF reduces the cross-field particle transport primarily by suppressing the density fluctuation as well as decorrelating density and potential fluctuations. V C 2015 AIP Publishing LLC.

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Intermittent transport in the scrape-off layer of the SINP tokamak

Saha

Chowdhury

2006

Physics of Plasmas

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Plasma structures, localized in the two-dimensional poloidal cross section propagating radially and poloidally, have been detected in the scrape-off layer of the SINP tokamak. Structures with densities both higher and lower than the density of the background plasma are present, with electron temperatures higher and lower, respectively, than that of the background plasma. These are responsible for the large and sporadic bursts of particle flux to the wall, amounting to 30%–40% of the total cross-field flux. These intermittent structures also cause the probability distribution function of the fluctuations to deviate from the Gaussian behavior, especially away from the limiter.

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Effect of poloidal velocity shear on the edge fluctuations in the SINP tokamak

Cited by 7 publications

References 38 publications

Intermittent Bursts in the Boundary Plasma of HT-7

Intermittent Bursts in the Boundary Plasma of HT-7

Observation of fluctuation-driven particle flux reduction by low-frequency zonal flow in a linear magnetized plasma

Intermittent transport in the scrape-off layer of the SINP tokamak

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