A brief review: experimental investigation of zonal flows and geodesic acoustic modes in fusion plasmas

Zhao, K.J.; Dong, J. Q.; Li, J Q; Yan, L.W.

doi:10.1088/2058-6272/aad382

Cited by 5 publications

(8 citation statements)

References 104 publications

(149 reference statements)

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“…Although there are several mechanisms that could lead to triggering the L-H transition, cf [531], it is the role of turbulence driven flows that is of interest here. While RS driven flows ṽr ṽθ seem too small in L-mode to create a critical shear alone (cf [64]), when combined with a 'baseline' equilibrium mean flow shear, RS flows may take the role of a trigger. RS is indeed observed to increase prior to the L-H transition in many experiments.…”

Section: L-h Transitionmentioning

confidence: 99%

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Geodesic acoustic modes in magnetic confinement devices

Smolyakov

Ido

2021

Nucl. Fusion

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Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature—an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments.

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Section: L-h Transitionmentioning

confidence: 99%

“…There is also a collection of papers on ZFs in a special section of the April 2006 issue of Plasma Physics and Controlled Fusion [62]. More recently there have been a couple of brief reviews of GAMs with emphasis on kinetic theory [63] and its application to experiment [64].…”

Section: Introductionmentioning

confidence: 99%

Geodesic acoustic modes in magnetic confinement devices

Smolyakov

Ido

2021

Nucl. Fusion

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“…To analyze the parametric dependence of the ZF growth rate based on equation (10), the formulas of real frequency and linear growth rate of CTEM instability in the presence of α particles are also needed, which have been derived in previous work [19]. So we just show them directly…”

Section: Expression For Ctem Driven Zf Growth Ratementioning

confidence: 99%

“…τ eD = τ eT = τ ei . Substituting equation ( 13) into equation (10), we get the normalized ZF growth rate…”

Section: Andmentioning

confidence: 99%

Effects of alpha particles on the CTEM driven zonal flow in deuterium–tritium tokamak plasmas

Sadam¹,

Guo²,

Wang³

2022

Nucl. Fusion

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The effects of fusion-born alpha (α) particles on zonal flow (ZF) driven by collisionless trapped electron mode (CTEM) turbulence are analytically investigated, using gyrokinetic and bounce kinetic theories in the deuterium-tritium (D-T) tokamak plasmas. It is found that ZF growth rate is increased by α particles because of the reduction of polarization shielding as well as enhancement of CTEM instability. The results of this paper are qualitatively consistent with the enhancement of the level of residual ZF by α particles in [Y.W. Cho and T.S. Hahm, Nucl. Fusion 59, 066026 (2019)]. The parametric dependence of ZF growth rate is also analyzed. The increment of ZF growth rate is further enhanced by α particles with higher fraction and steeper density profile. Besides, the dependence of ZF growth rate on electron temperature T_e could be changed qualitatively by the presence of α particles when T_i=T_e. Moreover, the difference of ZF growth rates in the presence of α particles with slowing down (SD) and equivalent Maxwellian (EM) distribution functions is very weak. These results could be very important for accurate prediction of the confinement in the future burning plasmas such as International Thermonuclear Experimental Reactor (ITER) and China Fusion Engineering Test Reactor (CFETR).

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“…[20] It is well recognized that zonal flows self-generated by turbulence play an important role in regulating turbulence, reducing transport level, and thus improve plasma confinement in fusion plasmas. [21,22] Moreover, zonal flows can not only stabilize the fluctuations through flow shear but also play a major role in turbulence saturation. Such dynamics usually occur in the turbulence with single drive force in a limited spectral range.…”

Section: Introductionmentioning

confidence: 99%

Role of the zonal flow in multi-scale multi-mode turbulence with small-scale shear flow in tokamak plasmas

Li¹,

Li²,

Wang³

et al. 2022

Chinese Phys. B

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The structural characteristics of zonal flows and their roles in the nonlinear interaction of multi-scale multi-mode turbulence are investigated numerically via a self-consistent Landau-fluid model. The multi-mode turbulence here is composed of a shorter wavelength electromagnetic (EM) ion temperature gradient (ITG) mode and a Kelvin-Helmholtz (KH) instability with long wavelengths excited by externally imposed small-scale shear flows. For strong shear flow, a prominent periodic intermittency of fluctuation intensity except for dominant ITG component is revealed in turbulence evolution, which onset time depends on the ion temperature gradient and the shear flow amplitudes corresponding to different KH instabilities. It is identified that the intermittency phenomenon results from the zonal flow dynamics, which is mainly generated by the KH mode and back-reacts on it. It is demonstrated that the odd symmetric components of zonal flow (same symmetry as the external flow) make the radial parity of the KH mode alteration through adjusting the drift velocities at two sides of the resonant surface so that the KH mode becomes bursty first. Afterwards, the ITG intermittency follows due to nonlinear mode coupling. Parametric dependences of the features of the intermittency are elaborated. Finally, associated turbulent heat transport is evaluated.

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A brief review: experimental investigation of zonal flows and geodesic acoustic modes in fusion plasmas

Cited by 5 publications

References 104 publications

Geodesic acoustic modes in magnetic confinement devices

Geodesic acoustic modes in magnetic confinement devices

Effects of alpha particles on the CTEM driven zonal flow in deuterium–tritium tokamak plasmas

Role of the zonal flow in multi-scale multi-mode turbulence with small-scale shear flow in tokamak plasmas

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