Experimental progress on zonal flow physics in toroidal plasmas

Fujisawa, A.; Ido, T.; Shimizu, A.; Okamura, S.; Matsuoka, K.; Iguchi, H.; Hamada, Y.; Nakano, H.; Ohshima, S.; Itoh, K.; Hoshino, K.; Shinohara, K.; Miura, Y.; Nagashima, Yoshihiko; Itoh, Sanae I.; Shats, Michael; Xia, Hua; Dong, J. Q.; Yan, Lei; Zhao, K.J.; Conway, G. D.; Stroth, U.; Melnikov, A. V.; Eliseev, L.G.; Лысенко, С. Е.; Perfilov, S.V.; Hidalgo, C.; Tynan, G. R.; Holland, C.; Diamond, P. H.; McKee, G. R.; Fonck, R. J.; Gupta, D.; Schoch, P. M.

doi:10.1088/0029-5515/47/10/s19

Cited by 114 publications

(111 citation statements)

References 51 publications

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“…This EM differs in various features (radial location, mode structure, absence of magnetic component) from other types of quasicoherent modes, earlier found in TJ-II [6,7,[23][24][25] in higher density plasmas, or from energetic particle modes found in other machines [8][9][10][11]. The EM also differs from GAMs [26,27], which have different features. More in particular, the EM fulfills the Boltzmann relationship with k B ∼ 1, unless have same frequency range.…”

Section: Discussion and Summarymentioning

confidence: 67%

A Quasi-Coherent Electrostatic Mode in ECRH Plasmas on TJ-II

Melnikov

Eliseev

Ochando³

et al. 2011

Plasma and Fusion Research

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A new type of instability mode, related to suprathermal electrons, was found in extremely low-density plasmas, (n e = (0.2-0.5) × 10 19 m −3 ) with electron cyclotron resonance heating and current drive (ECRH/ECCD) in the TJ-II heliac. The quasi-monochromatic density and plasma potential oscillations in the frequency range 20-120 kHz tend to have several "branches" with constant frequency shift between them. The typical amplitude of the mode induced potential oscillations was estimated to be Δϕ EM ∼ 20 V. The mode branches have an individual and finite radial extent, odd low poloidal structure (m ≤ 5) and angular phase velocity of poloidal rotation of about 8 × 10 4 rad/s in the ion diamagnetic drift direction. The contribution of the mode to the turbulent particle flux Γ E×B for the observed wave vectors k θ < 3 cm −1 was found to be small in comparison with the contribution from broadband turbulence.

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Section: Discussion and Summarymentioning

confidence: 67%

A Quasi-Coherent Electrostatic Mode in ECRH Plasmas on TJ-II

Melnikov

Eliseev

Ochando³

et al. 2011

Plasma and Fusion Research

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“…The ion sound speed over the geometric major radius R o scaling has been demonstrated on several devices (c.f. [36]), including the appropriate ion mass variation between hydrogen, deuterium and helium plasmas [18]. However, figure 3(a) also shows a clear inverse dependence on the plasma elongation.…”

Section: Gam Shape Dependencementioning

confidence: 94%

Frequency scaling and localization of geodesic acoustic modes in ASDEX Upgrade

Conway

Tröster

Scott

et al. 2008

Plasma Phys. Control. Fusion

110

163

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Abstract. The frequency behaviour and localization of the geodesic acoustic mode (GAM), believed to be a coherent plasma turbulence-generated E r × B T zonal flow oscillation, is studied in the ASDEX Upgrade tokamak using Doppler reflectometry. In typical elongated (1.4 < κ < 1.75) plasmas with an X-point divertor configuration the GAM is observed only in the edge density gradient region 0.95 < ρ pol < 1.0 between the density pedestal top and the flux surface boundary. The GAM frequency (5 − 25 kHz) is found to scale linearly as ω = G c s /R o (sound speed over major radius) but with an inverse dependence on the plasma elongation κ and a weak direct dependence on the safety factor q. The lower the GAM frequency the more important it is expected to become in moderating the turbulence via shear decorrelation. A heuristic scaling law for the frequency scale factor G ∼ O(1) involving κ and finite aspect ratio terms has been obtained from dedicated parameter scans. For circular plasmas κ ∼ 1 touching the limiter the density pedestal is weakened and the GAM is seen to reach in radially as far as ρ pol ∼ 0.75, depending on the q profile, with a frequency scale G → √ 2 consistent with theoretical predictions. Radially the GAM frequency is not a smooth function but displays a series of plateaus a few cm wide coinciding with peaks in the GAM amplitude, suggesting several zonal flow layers. At the plateau edges the GAM spectral peak splits into two frequency branches.

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“…There is much linear study on GAM's damping due to collision and ion Landau resonance [8][9][10][11][12][13][14][15][16] and on GAM's radial propagation due to finite thermal ion gyroradius and plasma temperature profile inhomogeneity [13,14]. Nonlinear studies found that that GAM can be driven by plasma microturbulence [13,[17][18][19], consistent with experimental observation of GAM in the plasma edge region [20][21][22]. Recently, Sasaki et al showed that self-interaction of turbulence-induced GAMs can drive both second harmonic [23] and zonal flow sideband [24].…”

Section: Introductionmentioning

confidence: 53%

On Nonlinear Self-interaction of Geodesic Acoustic Mode Driven By Energetic Particles

Fu¹

2010

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It is shown that nonlinear self-interaction of energetic particle-driven Geodesic Acoustic Mode does not generate a second harmonic in radial electric field using the fluid model. However, kinetic effects of energetic particles can induce a second harmonic in the radial electric field. A formula for the second order plasma density perturbation is derived. It is shown that a second harmonic of plasma density perturbation is generated by the convective nonlinearity of both thermal plasma and energetic particles. Near the midplane of a tokamak, the second order plasma density perturbation (the sum of second harmonic and zero frequency sideband) is negative on the low field side with its size comparable to the main harmonic at low fluctuation level. These analytic predictions are consistent with the recent experimental observation in DIII-D.

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Experimental progress on zonal flow physics in toroidal plasmas

Cited by 114 publications

References 51 publications

A Quasi-Coherent Electrostatic Mode in ECRH Plasmas on TJ-II

A Quasi-Coherent Electrostatic Mode in ECRH Plasmas on TJ-II

Frequency scaling and localization of geodesic acoustic modes in ASDEX Upgrade

On Nonlinear Self-interaction of Geodesic Acoustic Mode Driven By Energetic Particles

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