Geodesic Acoustic Eigenmodes

Itoh, K.; Itoh, Sanae I.; Diamond, P. H.; Fujisawa, A.; Yagi, M.; Watari, T.; Nagashima, Yoshihiko; Fukuyama, A.

doi:10.1585/pfr.1.037

Cited by 59 publications

(88 citation statements)

References 15 publications

(28 reference statements)

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“…From the radial structure of global GAM eigenmodes [5] in non-local (non-Boussinesq) computations we deduce a nonlinear, i.e. turbulence induced, dispersion relation.…”

mentioning

confidence: 94%

“…2 a) confirms the obtained dispersion relation. The above values for α can be used to estimate the radial extent of a global eigenmode whose radial structure is on one hand given by an Airy function [5]. On the other hand the turbulence excites GAMs only in a limited range of radial wave numbers, whose distribution is assumed to be a Gaussian of width σ k centered at k r = k 0 .…”

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confidence: 99%

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The nonlinear dispersion relation of geodesic acoustic modes

Hager

Hallatschek

2012

Physics of Plasmas

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The energy input and frequency shift of geodesic acoustic modes (GAMs) due to turbulence in tokamak edge plasmas are investigated in numerical two-fluid turbulence studies. Surprisingly, the turbulent GAM dispersion relation is qualitatively equivalent to the linear GAM dispersion but can have drastically enhanced group velocities. In up-down asymmetric geometry the energy input due to turbulent transport may favor the excitation of GAMs with one particular sign of the radial phase velocity relative to the magnetic drifts and may lead to pulsed GAM activity.

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“…From the radial structure of global GAM eigenmodes [5] in non-local (non-Boussinesq) computations we deduce a nonlinear, i.e. turbulence induced, dispersion relation.…”

mentioning

confidence: 94%

mentioning

confidence: 99%

The nonlinear dispersion relation of geodesic acoustic modes

Hager

Hallatschek

2012

Physics of Plasmas

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“…In earlier work [12,13], the GAMs turned out to be standing waves with a frequency-dispersion ≃ √ 2 + 1/ 2 /2 , where , and are the sound speed, major radius and safety factor, respectively. In recent work, the radial propagation of GAMs and GAM eigenmodes have been discussed by several authors [14][15][16][17][18], but no general rules have been given for the direction and velocity of the GAM propagation. The experimental observation on the GAM propagation has rarely been reported either.…”

Section: Introductionmentioning

confidence: 99%

Observation of geodesic acoustic modes (GAMs) and their radial propagation at the edge of the TEXTOR tokamak

Xu¹,

Shesterikov²,

Schoor³

et al. 2011

Plasma Phys. Control. Fusion

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The electrostatic potential and density fluctuations have been measured at the edge of TEXTOR tokamak by two toroidally distant Langmuir probe arrays. The geodesic acoustic mode (GAM) zonal flows are observed in potential fluctuations with a toroidal and poloidal symmetric structure.The GAM frequency, , changes monotonically with the local temperature and is close to the frequency-dispersion predicted by theories. Bispectral analysis shows clear nonlinear coupling between the GAM and broadband ambient turbulence. The GAM packet has a narrow radial extent with ≃ (0.5 − 0.7) cm −1 and exhibits explicitly a radially outward propagation. Furthermore, the radial correlation structure of GAMs and their radial propagation have been investigated in a wide range of parameters by varying plasma density (¯0=(1.5-3.0)×10 19 m −3 ) and edge safety factor (5.0 ≤ ( ) ≤ 5.9). It is found that the magnitude of the GAM correlations reduces remarkably with the increase of the plasma density as approaching to the density-limit, while the radial wavelength of GAMs only decreases slightly in higher density and larger ( ) discharges.With increasing plasma density, the radial propagating phase speed of GAMs is strongly reduced along with the drop of the local temperature. The results provide new evidence on the propagation properties of GAM zonal flows.2

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“…Radial propagation of geodesic acoustic modes (GAMs) [1], and GAM eigenmodes have been discussed in recent literature [2][3][4]. The existence and properties of global GAM eigenmodes, which are influenced by the GAM group velocity, might be relevant for the efficiency of GAM excitation [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…The existence and properties of global GAM eigenmodes, which are influenced by the GAM group velocity, might be relevant for the efficiency of GAM excitation [4,5]. This, in turn, could affect turbulent transport due to the potential role of GAMs in nonlinear turbulence saturation [6].…”

Section: Introductionmentioning

confidence: 99%

Radial propagation of geodesic acoustic modes in up-down asymmetric magnetic geometries

Hager

Hallatschek

2010

Physics of Plasmas

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The energy approach to the analysis of the propagation of geodesic acoustic modes presented in Physics of Plasmas 16, 072503 (2009) is generalized to up-down asymmetric magnetic geometries including a model for single-null configuration. By removing the neoclassical cancellation effects, updown asymmetry can trigger a non-vanishing group velocity at zero radial wavenumber. Theoretical insight in this effect is provided by analytical calculations combined with numerical gyrokinetic and two-fluid studies. Thereby, an useful estimate of the group velocity at zero radial wavenumber is derived within a two-fluid framework.

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Geodesic Acoustic Eigenmodes

Cited by 59 publications

References 15 publications

The nonlinear dispersion relation of geodesic acoustic modes

The nonlinear dispersion relation of geodesic acoustic modes

Observation of geodesic acoustic modes (GAMs) and their radial propagation at the edge of the TEXTOR tokamak

Radial propagation of geodesic acoustic modes in up-down asymmetric magnetic geometries

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