Investigation of the geodesic acoustic mode in EAST H-mode operation using Doppler backscattering systems

Zhou, C.; Liu, A.D.; Liu, Z.Y.; Wang, M.Y.; Xi, Fu; Zhang, Jun; Ji, J.; Fan, H.R.; Shi, Tonghui; Liu, H.Q.; Wang, S.X.; Zhuang, G.; Li, H.; Lan, Tao; Xie, Jinlin; Mao, Wenzhe; Ding, Weixing; Zou, X.L.; Liu, W.D.

doi:10.1088/1741-4326/aad249

Cited by 13 publications

(18 citation statements)

References 37 publications

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“…Here, we have to allow for the mode resonances with the ion transit motion so that ω v /qR 0 ω d . Then, one finds from (42) for the perturbed distribution function in the form f = f c cos θ + f s sin θ:…”

Section: Transit Resonance (Landau) and Coupling To The Ion Soundmentioning

confidence: 99%

“…Turbulence driven GAMs have now been ubiquitously observed in ohmic and low-confinement L-mode plasmas in many devices, but not in strong high-confinement H-mode plasmas-although recent results suggest GAMs may form in weak H-modes where the edge turbulence level has recovered sufficiently [42]. The detection of GAMs also requires suitable diagnostics with sufficient sensitivity, and of course GAMs of measurable amplitude.…”

Section: Introductionmentioning

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: Transit Resonance (Landau) and Coupling To The Ion Soundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Geodesic acoustic modes in magnetic confinement devices

Smolyakov

Ido

2021

Nucl. Fusion

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“…19(c), very similar to experimental measures of GAM intermittency. [25,[37][38][39][40][41][42][43][44]…”

Section: Nonlinear Coupling Between Multiple Central Rational Surface...mentioning

confidence: 99%

The intermittent excitation of geodesic acoustic mode by resonant Instanton of electron drift wave envelope in L-mode discharge near tokamak edge

Li¹,

Zhang²,

Mahajan³

et al. 2022

Chinese Phys. B

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There are two distinct phases in the evolution of drift wave envelope in the presence of zonal flow. A long-lived standing wave phase, which we call the Caviton, and a short-lived traveling wave phase (in radial direction) we call the Instanton. Several abrupt phenomena observed in tokamaks, such as intermittent excitation of geodesic acoustic mode (GAM) shown in this paper, could be attributed to the sudden and fast radial motion of Instanton. The composite drift wave – zonal flow system evolves at the two well-separate scales: the micro and the meso-scale. The eigenmode equation of the model defines the zero order (micro-scale) variation; it is solved by making use of the two dimensional (2D) weakly asymmetric ballooning theory (WABT), a theory suitable for modes localized to rational surface like drift waves, and then refined by shifted inverse power method, an iterative finite difference method. The next order is the equation of electron drift wave (EDW) envelope (containing group velocity of EDW) which is modulated by the zonal flow generated by Reynolds stress of EDW. This equation is coupled to the zonal flow equation, and numerically solved in spatiotemporal representation; the results are displayed in self-explanatory graphs. One observes a strong correlation between the Caviton-Instanton transition and the zero-crossing of radial group velocity of EDW. The calculation brings out the defining characteristics of the Instanton: it begins as a linear traveling wave right after the transition. Then, it evolves to a nonlinear stage with increasing frequency all the way to 20 kHz. The modulation to Reynolds stress in zonal flow equation brought in by the nonlinear Instanton will cause resonant excitation to GAM. The intermittency is shown due to the random phase mixing between multiple central rational surfaces in the reaction region.

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“…In the past decades, a multitude of magnetic fusion devices including tokamaks and stellarators, such as MAST [5], DIII-D [6], ASDEX-U [7], KSTAR [8], EAST [9], HL-2A [10], Tore Supra [11], TJ-II [12] and LHD [13], have been equipped with DBS diagnostics. In these devices, the DBS diagnostics have empowered researchers to observe a diversity of turbulence-related phenomena, such as Trapped Electron Modes (TEM) [14], Electron Temperature Gradient (ETG) modes [15], Geodesic Acoustic Modes (GAM) [16], zonal flows [17], Ion Cyclotron Emission (ICE) [18], Alfvén modes [19]. The widespread adoption of the DBS technique in plasma devices globally, and its versatility in facilitating a diverse of measurements including -from low to high-k fluctuations, to -1 -GAMs and zonal flows, and energetic particle driven coherent modes -underscores its instrumental role in advancing our understanding of plasma instabilities.…”

Section: Introductionmentioning

confidence: 99%

First data and preliminary experimental results from a new Doppler backscattering system on the MAST-U spherical tokamak

Shi,

Scannell,

Wen

et al. 2023

J. Inst.

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A new Doppler backscattering (DBS) system, consisting of Q-band and V-band, has been installed and achieved its first data on the MAST-U spherical tokamak. The Q-band and V-band have separate microwave source systems, but share the same optical front-end components. The Q-band and V-band sources simultaneously generate eight (34, 36, 38, 40, 42, 44, 46 and 48 GHz) and seven (52.5, 55, 57.5, 60, 62.5, 65 and 67.5 GHz) fixed frequency probe beams, respectively. These frequencies provide a large range of radial positions from the low-field-side edge plasma to the core, and possibly to the high-field-side edge, depending on the plasma conditions. The quasi-optical system consists of a remotely-tunable polarizer, a focusing lens and a remotely-steerable mirror. By steering the mirror, the system provides remote control of the probed density fluctuation wavenumber, and allow the launch angle to match the magnetic field. The range of accessible turbulence wavenumbers (kθ ) is reasonably large with normalized wavenumber kθρs ranging from <0.5 to 9. The first data acquired by this DBS system is validated by comparing with the data from the other DBS system on MAST-U (introduced in ref. [21]). An example of measuring the velocity profile spanning from the edge to the center in a high-density plasma is presented, indicating the robust capabilities of the integrated Q-band and V-band DBS systems.

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Investigation of the geodesic acoustic mode in EAST H-mode operation using Doppler backscattering systems

Cited by 13 publications

References 37 publications

Geodesic acoustic modes in magnetic confinement devices

Geodesic acoustic modes in magnetic confinement devices

The intermittent excitation of geodesic acoustic mode by resonant Instanton of electron drift wave envelope in L-mode discharge near tokamak edge

First data and preliminary experimental results from a new Doppler backscattering system on the MAST-U spherical tokamak

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