Effects of Er shear on edge turbulence of the China Tokamak-6B

Wang, Guiding; Yang, Xiaomin; Chi, Feng; Jiang, Diming; Zhou, Baosuo; Qi, Xin; Wang, Long

doi:10.1063/1.872792

Cited by 7 publications

(2 citation statements)

References 40 publications

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“…Figure 8(b) shows that the magnitude of fluctuation levels of positive biasing is higher than w/o biasing figure 8(a), whereas in the case of negative biasing figures 8(c) and (d) the fluctuation levels are smaller than w/o bias case. Similar phenomena are also seen experimentally in references [52,53], therefore, our results match at least qualitatively with the experimental fact. The higher level of density fluctuations in the case of positive biasing (+64 volt) may increase instability and radial transport.…”

Section: Simulation Resultssupporting

confidence: 93%

Edge biasing and its impact on the edge and SOL turbulence

Shankar¹,

Bisai²,

Raj³

et al. 2022

Nucl. Fusion

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A theoretical study is made of the effect of edge biasing on the dynamics of the interchange turbulence in the edge and scrape-off layer (SOL) regions. A linear analysis of a set of model fluid equations shows that biasing stabilizes the small ky modes. The model equations are next solved numerically, using the BOUT++ framework, to explore the nonlinear dynamics in the presence of positive or negative bias and compared to results in the absence of bias. Positive biasing is found to lead to a larger increment in plasma density and temperature as compared to negative biasing. It is further observed that cross-correlation between density and poloidal electric field at different radial positions decreases for positive biasing and in the case of negative biasing it is almost similar to that of no biasing. Plasma density and poloidal electric field fluctuations have been investigated which show that the density fluctuations increase (decrease) for positive (negative) biasing but the radially outward flux for these biasing cases always decreases mainly due to the decrease of cross-correlation between density and poloidal electric field fluctuations.

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Section: Simulation Resultssupporting

confidence: 93%

Edge biasing and its impact on the edge and SOL turbulence

Shankar¹,

Bisai²,

Raj³

et al. 2022

Nucl. Fusion

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“…There is accumulating evidence that E؋B shear suppression of turbulence is the most likely mechanism to be responsible for various forms of confinement enhancement. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The theory of E؋B shear suppression was first developed in cylindrical geometry. 17 It is valid when the time variation of E r is much slower than the eddy turn-over time.…”

Section: Introductionmentioning

confidence: 99%

Shearing rate of time-dependent E×B flow

et al. 1999

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Theory of E؋B shear suppression of turbulence in toroidal geometry ͓Phys. Plasmas 2, 1648 ͑1995͔͒ is extended to include fast time variations of the E؋B flows often observed in nonlinear simulations of tokamak turbulence. It is shown that the quickly time varying components of the E؋B flows, while they typically contribute significantly to the instantaneous E؋B shearing rate, are less effective than the slowly time varying components in suppressing turbulence. This is because the shear flow pattern changes before eddies get distorted enough. The effective E؋B shearing rate capturing this important physics is analytically derived and estimated from zonal flow statistics of gyrofluid simulation. This provides new insights into understanding recent gyrofluid and gyrokinetic simulations that yield a reduced, but not completely quenched, level of turbulence in the presence of turbulence-driven zonal flows.

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Zonal flow dynamics and anomalous transport

2005

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Nonlinear equations for the slow space-time evolution of the radial drift wave-ion-temperature gradient (DW-ITG) envelope and zonal flow (ZF) amplitude have been derived within a coherent four-wave drift wave-zonal flow model. In the local limit this model demonstrates spontaneous generation of zonal flow and nonlinear drift wave-zonal flow dynamics in toroidal plasmas. The model allows slow temporal and spatial variations of the DW-ITG radial envelope, incorporating the effects of equilibrium variations, i.e., turbulence spreading and size dependence of the saturated wave intensities and transport coefficients. The competition between linear drive/damping and drift wave spreading due to linear and nonlinear group velocities and nonlinear energy transfer between DW and ZF determines the saturation levels of the fluctuating fields. The turbulence intensity level exhibits a transition from Bohm scaling at small system size (Lp∕ρi) to gyro-Bohm for large system size. This system exhibits chaotic behavior and intermittency, depending on system size and proximity to marginal stability.

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Effects of Er shear on edge turbulence of the China Tokamak-6B

Cited by 7 publications

References 40 publications

Edge biasing and its impact on the edge and SOL turbulence

Edge biasing and its impact on the edge and SOL turbulence

Shearing rate of time-dependent E×B flow

Zonal flow dynamics and anomalous transport

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