Flux-surface shaping effects on tokamak edge turbulence and flows

Kendl, A.; Scott, B.

doi:10.1063/1.2158695

Cited by 45 publications

(47 citation statements)

References 54 publications

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“…The first candidate is the magnetic shear (s = dq/dr), which increases in the edge with κ b . Enhanced magnetic shear damping of the turbulence was proposed by Kendl as the major cause of the reciprocal decrease in turbulent transport observed in gyro-fluid numerical simulations with increasing κ [30]. Also, while collisionless damping, γ ∝ exp(−q 2 ), maybe dominant in the core, the effect of collisional damping (with a weaker q dependence: γ ∝ ν ii /q) is certainly evident in the edge where the GAM disappears at high densities (ν * ∝ n/T 2 ).…”

Section: Summary and Discussionmentioning

confidence: 99%

Amplitude behaviour of geodesic acoustic modes in the ASDEX Upgrade tokamak

Conway

2008

Plasma Phys. Control. Fusion

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Abstract. The amplitude behaviour of the geodesic acoustic mode (GAM), a low frequency (5 − 25 kHz) coherent plasma turbulence-generated E r × B zonal flow oscillation, is studied in the ASDEX Upgrade tokamak using Doppler reflectometry. Across the tokamak edge the GAM displays one or more maxima a few cm wide, coinciding with radial plateaus in the GAM frequency, suggesting nested zonal flow layers. The GAM peak amplitude ranges between 0.2 − 0.8 km s −1 , corresponding to several tens of percent of the mean E × B flow velocity. In limiter configurations the GAM amplitude is found to decrease inversely with the plasma vertical elongation 1.1 < κ < 1.4, but rises again in X-point divertor configurations at higher κ ∼ 1.6. At low κ the GAM amplitude increases with the safety factor q, consistent with damping effects, but becomes less sensitive to q at high κ. A positive linear dependence on the electron temperature gradient, an indicator of the linear turbulence drive, is also observed.

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Section: Summary and Discussionmentioning

confidence: 99%

Amplitude behaviour of geodesic acoustic modes in the ASDEX Upgrade tokamak

Conway

2008

Plasma Phys. Control. Fusion

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“…For the present geometry, B u ¼ ðB 0 R 0 Þ=R 2 c and B h Ã ¼ w 0 =J . Using the covariant and contravariant components of the metric tensor and the magnetic field as well as the derivatives of these coefficients, the coefficients in the operators (18) to (21) can be analytically obtained. Their detailed expressions are given in Appendix B for both toric and flux tube coordinate systems.…”

Section: Circular Magnetic Flux Surfaces With Aspect Ratio Effectsmentioning

confidence: 99%

“…16 Aspect ratio effects are thought to play an important role in determining the characteristic crosssectional area of the SOL and explain in part the improvement of confinement when moving the toroidal limiter from the low-field-side to the high-field-side of the tokamak. 17 In the plasma edge, a reduction of transport due to elongation is observed in gyrofluid turbulence, 18 while some aspect ratio effects in collisional drift wave turbulence are briefly discussed in Ref. 19.…”

Section: Introductionmentioning

confidence: 99%

Aspect ratio effects on limited scrape-off layer plasma turbulence

et al. 2014

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The drift-reduced Braginskii model describing turbulence in the tokamak scrape-off layer is written for a general magnetic configuration with a limiter. The equilibrium is then specified for a circular concentric magnetic geometry retaining aspect ratio effects. Simulations are then carried out with the help of the global, flux-driven fluid three-dimensional code GBS [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. Linearly, both simulations and simplified analytical models reveal a stabilization of ballooning modes. Nonlinearly, flux-driven nonlinear simulations give a pressure characteristic length whose trends are correctly captured by the gradient removal theory [Ricci and Rogers, Phys. Plasmas 20, 010702 (2013)], that assumes the profile flattening from the linear modes as the saturation mechanism. More specifically, the linear stabilization of ballooning modes is reflected by a 15% increase in the steady-state pressure gradient obtained from GBS nonlinear simulations when going from an infinite to a realistic aspect ratio. V C 2014 AIP Publishing LLC. [http://dx

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“…In Ref. [32], the difference of the geodesic energy transfer from low frequency zonal flows to GAMs is discussed in regard to plasmas with and without an X point of the magnetic separatrix. The existence of the X point becomes geodesic curvature small, and as a result, the geodesic transfer in diverter plasmas could be smaller than that in limiter plasmas.…”

Section: Results Of Bispectral Analysismentioning

confidence: 99%

Experimental Study of Nonlinear Processes in Edge Turbulence of Toroidal Plasmas

Nagashima

Hoshino

Nagaoka

et al. 2006

Plasma and Fusion Research

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This paper presents experimental studies of nonlinear processes between meso-scale structures and turbulent fluctuations, by use of bispectral analysis, in the edge region of toroidal plasmas. In ohmically heated plasmas of the JFT-2M tokamak, the drift wave-zonal flow system is investigated by observation of the potential fluctuations. The total bicoherence is composed of two components, i.e., the peak at the geodesic acoustic mode (GAM) frequency and broadband distribution. The biphase is also obtained, which indicates the phase angle of coherent interaction between GAM oscillations and broadband fluctuations. Bispectral functions (e.g., magnitude and phase) give an order-of-estimate agreement for the drift wave-zonal flow systems. Bicoherence analysis is also applied to the edge plasmas of the high-confinement mode (H-mode) of the Compact Helical System (CHS). In the case of CHS plasmas, nonlinear couplings in a system composed of coherent global magneto-hydrodynamic (MHD) oscillations and broadband fluctuations (up to hundreds kHz range) have been observed. Bispectral analysis enhances our understanding of the self-regulation systems of various toroidal plasmas in which strong turbulence and meso-scale structures coexist.

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Flux-surface shaping effects on tokamak edge turbulence and flows

Cited by 45 publications

References 54 publications

Amplitude behaviour of geodesic acoustic modes in the ASDEX Upgrade tokamak

Amplitude behaviour of geodesic acoustic modes in the ASDEX Upgrade tokamak

Aspect ratio effects on limited scrape-off layer plasma turbulence

Experimental Study of Nonlinear Processes in Edge Turbulence of Toroidal Plasmas

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