Electromagnetic effects of kinetic geodesic acoustic mode in tokamak plasmas

Wang, Lingfeng; Dong, J. Q.; Shen, Yong; He, Huimin

doi:10.1063/1.3590892

Cited by 25 publications

(42 citation statements)

References 24 publications

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“…This system of equations can be used to describe the complete nonlinear dynamics of GAMs using a reduced drift-Braginskii description including the effects of finite β and collisionality. It is evident from the above equations that the GAM does contain m = 1 electromagnetic component which is in contrast to the previous Refs [40,41] …”

Section: Geodesic Acoustic Modecontrasting

confidence: 46%

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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Section: Geodesic Acoustic Modecontrasting

confidence: 46%

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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“…Magnetic perturbations due to GAMs are predicted for kinetic GAMs in low b (b ¼ plasma pressure/magnetic pressure) tokamak by taking into account finite Larmor radius, finite orbit width of the ions, and electron parallel dynamics. 48 Inclusion of finite b effects for radial eigenmode theory is desired for direct comparison with experimental observations. It should also be noted that recent energetic particle-induced GAM (EGAM) observations and theories 49-52 indicate a magnetic perturbation due to the GAMs.…”

Section: Discussion and Summarymentioning

confidence: 99%

Multi-field characteristics and eigenmode spatial structure of geodesic acoustic modes in DIII-D L-mode plasmas

et al. 2013

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The geodesic acoustic mode (GAM), a coherent form of the zonal flow, plays a critical role in turbulence regulation and cross-magnetic-field transport. In the DIII-D tokamak, unique information on multi-field characteristics and radial structure of eigenmode GAMs has been measured. Two simultaneous and distinct, radially overlapping eigenmode GAMs (i.e., constant frequency vs. radius) have been observed in the poloidal E×B flow in L-mode plasmas. As the plasma transitions from an L-mode to an Ohmic regime, one of these eigenmode GAMs becomes a continuum GAM (frequency responds to local parameters), while the second decays below the noise level. The eigenmode GAMs occupy a radial range of ρ = 0.6–0.8 and 0.75–0.95, respectively. In addition, oscillations at the GAM frequency are observed for the first time in multiple plasma parameters, including ne, Te, and Bθ. The magnitude of T̃e/Te at the GAM frequency (the magnitude is similar to that of ñe/ne) and measured ne–Te cross-phase (∼140° at the GAM frequency) together indicate that the GAM pressure perturbation is not determined solely by ñe. The magnetic GAM behavior, a feature only rarely reported, is significantly stronger (×18) on the high-field side of the tokamak, suggesting an anti-ballooning nature. Finally, the GAM is also observed to directly modify intermediate-wavenumber ñe levels (kρs ∼ 1.1). The simultaneous temperature, density, flow fluctuations, density-temperature cross-phase, and magnetic behavior present a new perspective on the underlying physics of the GAM.

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“…The GFLDR framework has also been used for implementing an extended version of the hybrid MHD gyrokinetic code HMGC [8,64], which simultaneously handles two generic initial particle distribution functions in the space of particle constants of motion. Applications of this eXtended HMGC (XHMGC) code [9,10] range from FTU electron fishbone to collective excitations of mesoscale Alfvénic fluctuations in FAST [11], for which detailed transport analyses have been carried out [14]. These investigations assume FAST equilibrium profiles as initial conditions, after the self-consistent dynamic formation of the FAST scenarios is obtained iteratively by interfacing several numerical tools: transport codes (JETTO and the CRONOS suite of codes, including NEMO and SPOT) and the ion cyclotron resonance heating (ICRH) full wave code TORIC, coupled with the quasi-linear solver SSFPQL, which accounts for both ICRH and negative neutral beam injection (NNBI) [14].…”

Section: Theory and Modelling Of Experimental Observationsmentioning

confidence: 99%

“…The GFLDR framework is also used for implementing an extended version of the hybrid MHD gyrokinetic code HMGC [8]. Applications of this eXtended HMGC (XHMGC) code [9,10] range from FTU electron fishbone to collective excitations of meso-scale Alfvénic fluctuations in FAST [11][12][13], for which detailed transport analyses have been carried out [14].…”

Section: Introductionmentioning

confidence: 99%

Overview of FTU results

Tuccillo¹,

Amicucci

Angelini³

et al. 2011

Nucl. Fusion

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New FTU ohmic discharges with a liquid lithium limiter at I P = 0.7–0.75 MA, B T = 7 T and n e0 ⩾ 5 × 1020 m−3 confirm the spontaneous transition to an enhanced confinement regime, 1.3–1.4 times ITER-97-L, when the density peaking factor is above a threshold value of 1.7–1.8. The improved confinement derives from a reduction of electron thermal conductivity (χe) as density increases, while ion thermal conductivity (χi) remains close to neoclassical values. Linear microstability reveals the importance of lithium in triggering a turbulent inward flux for electrons and deuterium by changing the growth rates and phase of the ion-driven turbulence, while lithium flux is always directed outwards. A particle diffusion coefficient, D ∼ 0.07 m2 s−1, and an inward pinch velocity, V ∼ 0.27 m s−1, in qualitative agreement with Bohm–gyro-Bohm predictions are inferred in pellet fuelled lithized discharges. Radio frequency heated plasmas benefit from cleaner plasmas with edge optimized conditions. Lower hybrid waves penetration and current drive effects are clearly demonstrated at and above ITER densities thanks to a good control of edge parameters obtained by plasma operations with the external poloidal limiter, lithized walls and pellet fuelling. The electron cyclotron (EC) heating system is extensively exploited in FTU for contributing to ITER-relevant issues such as MHD control: sawtooth crash is actively controlled and density limit disruptions are avoided by central and off-axis deposition of 0.3 MW of EC power at 140 GHz. Fourier analysis shows that the density drop and the temperature rise, stimulated by modulated EC power in low collisionality plasmas are synchronous, implying that the heating method is the common cause of both the electron heating and the density drop. Perpendicularly injected electron cyclotron resonance heating is demonstrated to be more efficient than the obliquely injected one, reducing the minimum electric field required at breakdown by a factor of 3. Theoretical activity further develops the model to interpret high-frequency fishbones on FTU and other experiments as well as to characterize beta-induced Alfvén eigenmodes induced by magnetic islands in ohmic discharges. The theoretical framework of the general fishbone-like dispersion relation is used for implementing an extended version of the HMGC hybrid MHD gyrokinetic code. The upgraded version of HMGC will be able to handle fully compressible non-linear gyrokinetic equations and 3D MHD.

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Electromagnetic effects of kinetic geodesic acoustic mode in tokamak plasmas

Cited by 25 publications

References 24 publications

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

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

Multi-field characteristics and eigenmode spatial structure of geodesic acoustic modes in DIII-D L-mode plasmas

Overview of FTU results

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