Properties of Geodesic Acoustic Modes and the Relation to Density Fluctuations

Krämer‐Flecken, A.; Soldatov, S.; Koslowski, H. R.; Zimmermann, O.

doi:10.1103/physrevlett.97.045006

Cited by 90 publications

(125 citation statements)

References 14 publications

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“…These findings were confirmed by measurements with the hydrogen diagnostic beam RUDI [35]. Also the application of the upgraded reflectometer system allowed to observe geodesic acoustic modes in the plasma edge and resolve their role for density fluctuations and the impact of RMP on this important high frequency zonal flow domain [36]. The heat transport characteristics in the transition region between the stochastic layer and the core plasma, i.e.…”

Section: Resultssupporting

confidence: 59%

Application of advanced edge diagnostics for transport studies in the stochastic boundary of TEXTOR-DED

Schmitz¹,

Brezinsek²,

Classen

et al. 2008

AIP Conference Proceedings

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Abstract. In this paper the edge diagnostic equipment at the TEXTOR tokamak is described and its importance for detailed transport studies in different shapes of perturbed plasma edge layers is demonstrated. At TEXTOR an external resonant magnetic perturbation is induced by the dynamic ergodic divertor DED and various topologies of the perturbed magnetic field are feasible. A helical divertor topology, dominating magnetic island chains or an ergodicity dominated layer can be evoked adapting the perturbation field base mode number, the perturbation field strength and the plasma equilibrium. As unique feature the DED perturbation field can be rotated with frequencies of up to 10 kHz. The impact of the very different magnetic field structures and the fast rotation of the external perturbation field on local and global transport properties is analyzed here on selected examples from the various edge diagnostics with high time and / or high spatial resolution. Based on this basic knowledge the perturbed edge layer was adapted to control the particle exhaust characteristics and the impurity transport. Both, an improvement in the particle confinement was found as well as a controlled degradation -the so called particle pump out effect -correlated to a pronounced screening of impurities.

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Section: Resultssupporting

confidence: 59%

Application of advanced edge diagnostics for transport studies in the stochastic boundary of TEXTOR-DED

Schmitz¹,

Brezinsek²,

Classen

et al. 2008

AIP Conference Proceedings

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“…Linearizing the above set of equations (19)(20)(21)(22)(23)(24)(25), taking Fourier transforms and neglecting n , T i,e , one obtains the following dispersion relation…”

Section: A Linear Gam Dispersionmentioning

confidence: 99%

“…Otherwise they are excited by nonlinear processes like turbulent reynolds stresses [12][13][14][15][16][17][18], poloidally asymmetric particle fluxes [19] and heat fluxes [20]. Due to their finite frequency (usually a few kHz), distinct from that of broadband turbulence, GAMs are easier to detect, and thus have been observed on several tokamaks such as ASDEX Upgrade (AUG) [21] using Doppler backscattering (DBS), TEXTOR [22]using O-mode correlation reflectometer, and DIIID [23] using beam emission spectroscopy (BES). As of today, GAMS are observed in the majority of the tokamaks in the world including recent observations of GAMs in Tore Supra [24] using a DBS system.…”

Section: Introductionmentioning

confidence: 99%

Geodesic acoustic modes in a fluid model of tokamak plasma: the effects of finite beta and collisionality

Singh

Storelli

Gürcan

et al. 2015

Plasma Phys. Control. Fusion

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Starting from the Braginskii equations, relevant for the tokamak edge region, a complete set of nonlinear equations for the geodesic acoustic modes (GAM) has been derived which includes collisionality, plasma beta and external sources of particle, momentum and heat. Local linear analysis shows that the GAM frequency increases with collisionality at low radial wave number k r and decreases at high k r . GAM frequency also decreases with plasma beta. Radial profiles of GAM frequency for two Tore Supra shots, which were part of a collisionality scan, are compared with these calculations. Discrepency between experiment and theory is observed, which seems to be explained by a finite k r for the GAM when flux surface averaged density n and temperature T are assumed to vanish. It is shown that this agreement is incidental and self-consistent inclusion of n and T responses enhances the disagreement more with k r at high k r . So the discrepancy between the linear GAM calculation, (which persist also for more "complete" linear models such as gyrokinetics) can probably not be resolved by simply adding a finite k

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“…Thus, it is a powerful tool for the study of Zonal flow, which has a E r perturbation radially localized in toroidal plasmas [4,5,6]. Because of the flexibility of the diagnostic arrangements, the spatiotemporal characteristics of Zonal flows were obtained in both L-mode and H-mode plasmas [7,8,9,10], even the spatial distribution of GAM in density fluctuation was evidenced by poloidal correlation reflectometry [11].…”

Section: Introductionmentioning

confidence: 99%

Three Dimensional Measurements Of Radially Sheared Zonal Flows By Correlation Doppler Reflectometry

Zhong¹,

Shi²,

Xu³

et al. 2016

Proceedings of 1st EPS Conference on Plasma Diagnostics — PoS(ECPD2015)

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Correlation Doppler reflectometers have been newly developed in the HL-2A Tokamak. Owing to the flexibility of the diagnostic arrangements, the multi-channel systems allow us to study, simultaneously, the radial properties of edge turbulence and its long-range correlation in both the poloidal and toroidal direction. With correlation Doppler reflectometers, three-dimensional spatial structure of Geodesic Acoustic Mode (GAM) is surveyed, including the symmetric feature of poloidal and toroidal E r fluctuations, and the radial propagation of GAMs. The bi-coherence analysis for the E r fluctuations suggests that the three-wave nonlinear interaction could be the mechanism for the generation of GAM.The temporal behavior of GAM during the plasma density modulation experiments has been studied. The results show that the collisional damping plays a role in suppressing the GAM magnitudes, and hence, weakening the regulating effects of GAM on ambient turbulence. Three dimensional correlation Doppler measurements of GAM activity demonstrate that the newly developed correlation Doppler reflectometers in HL-2A are powerful tools for edge turbulence studies with high reliability. 1st EPS conference on Plasma Diagnostics

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Properties of Geodesic Acoustic Modes and the Relation to Density Fluctuations

Cited by 90 publications

References 14 publications

Application of advanced edge diagnostics for transport studies in the stochastic boundary of TEXTOR-DED

Application of advanced edge diagnostics for transport studies in the stochastic boundary of TEXTOR-DED

Geodesic acoustic modes in a fluid model of tokamak plasma: the effects of finite beta and collisionality

Three Dimensional Measurements Of Radially Sheared Zonal Flows By Correlation Doppler Reflectometry

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