Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations

Novikau, I.; Biancalani, A.; Bottino, A.; Gürcan, Özgür; Mänz, P.; Morel, Pierre; Poli, E.; Siena, A. Di

doi:10.1063/1.5003784

Cited by 15 publications

(21 citation statements)

References 49 publications

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“…For the damping rate, a higher value of the simulations with kinetic electrons is observed with respect to the simulations with adiabatic electrons, consistently with Ref. Biancalani et al (2014); Novikau et al (2017); Zhang & Lin (2010). No clear dependence on the electron mass is observed in this regime, where the variations with m e /m i are within the error bar.…”

Section: Gams For Pair Plasmasupporting

confidence: 86%

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Linear gyrokinetic studies with ORB5 en route to pair plasmas

et al. 2019

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The model of the global gyrokinetic particle-in-cell code ORB5 has been extended for the study of pair plasmas. This has been done by including the physics of the Debye shielding, by including the electron polarization density and by retaining the effects of the electron finite Larmor radius. This model is verified against previous numerical results for the cyclone base case tokamak scenario in deuterium plasmas, and for local pair plasma simulations. The linear dynamics of temperature-gradient driven instabilities and geodesic acoustic modes is investigated. Mass dependencies for different Debye lengths are studied.

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Section: Gams For Pair Plasmasupporting

confidence: 86%

“…2014; Novikau et al. 2017). For comparison, the result from a simulation of a deuterium plasma with adiabatic electrons is also shown in figure 8, as a red dashed line.…”

Section: Gams For Pair Plasmamentioning

confidence: 99%

Linear gyrokinetic studies with ORB5 en route to pair plasmas

et al. 2019

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“…A nonlinear origin of the "radially global" GAMs has also been recently suggested in Ref. [37]. Possible experimental evidence of such a complex self-regulating mechanism has recently been obtained in diverted discharges in TCV, where oscillations in the particle flux at the same GAM frequency have been observed [16].…”

Section: Discussionmentioning

confidence: 91%

Investigating the radial structure of axisymmetric fluctuations in the TCV tokamak with local and global gyrokinetic GENE simulations

Merlo

Brunner

Huang

et al. 2018

Plasma Phys. Control. Fusion

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Axisymmetric (n=0) density fluctuations measured in the TCV tokamak are observed to possess a frequency f0 which is either varying (radially dispersive oscillations) or a constant over a large fraction of the plasma minor radius (radially global oscillations) as reported in a companion paper [Z. Huang et al, this issue]. Given that f0 scales with the sound speed and given the poloidal structure of density fluctuations, these oscillations were interpreted as Geodesic Acoustic Modes, even though f0 is in fact smaller than the local linear GAM frequency fGAM. In this work we employ the Eulerian gyrokinetic code GENE to simulate TCV relevant conditions and investigate the nature and properties of these oscillations, in particular their relation to the safety factor profile. Local and global simulations are carried out and a good qualitative agreement is observed between experiments and simulations. By varying also the plasma temperature and density profiles, we conclude that a variation of the edge safety factor alone is not sufficient to induce a transition from global to radially inhomogeneous oscillations, as was initially suggested by experimental results. This transition appears instead to be the combined result of variations in the different plasma profiles, collisionality and finite machine size effects. Simulations also show that radially global GAM-like oscillations can be observed in all fluxes and fluctuation fields, suggesting that they are the result of a complex nonlinear process involving also finite toroidal mode numbers and not just linear global GAM eigenmodes.

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“…where the last step comes from expressing the element of the matrix G in terms of s and φ using Eq. (12). The integral over a shifted Maxwellian yields simply √ πφ.…”

Section: Wigner-function Treatmentmentioning

confidence: 99%

“…In particular, the importance of a kinetic treatment of the electrons was discussed e.g. in [10,11,12,13,14,15]. Meanwhile, gyrokinetic simulations can be considered as a standard tool to tackle both linear and nonlinear GAM-related problems [16,17,18,19,20,21].…”

Section: Introductionmentioning

confidence: 99%

Complex-Hamiltonian paraxial description of damped geodesic acoustic modes

et al. 2020

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Geodesic acoustic modes (GAMs) are a fundamental part of turbulence and zonal-flow dynamics in tokamaks. They exhibit simple yet non-trivial dispersive and dissipative properties. In linear numerical simulations, they are often initialized in the form of (e.g. Gaussian) packets which evolve in time. Depending on the parameters, dispersion and damping can act on comparable time scales during the GAM evolution. Wigner-function methods developed in the frame of non-Hermitian quantum mechanics are shown to be applicable to damped geodesic oscillations. In this approach, the standard approximation of "weak damping", often introduced for the treatment of plasma waves, is not needed. The method requires that the properties of the plasma do not vary significantly across the width of the packet (i.e. in the radial direction), so that a paraxial expansion of the underlying equations around the centre of the packet can be applied. For a quadratic Hamiltonian, the equations for the Wigner function governing the packet in the paraxial limit are shown to be equivalent to the equations of paraxial WKB theory (usually applied to the description of high-frequency wave beams in plasmas), with the real Hamiltonian replaced by the corresponding complex one. Analytic solutions are derived in particular cases and shown to agree with the results of global gyrokinetic simulations.

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Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations

Cited by 15 publications

References 49 publications

Linear gyrokinetic studies with ORB5 en route to pair plasmas

Linear gyrokinetic studies with ORB5 en route to pair plasmas

Investigating the radial structure of axisymmetric fluctuations in the TCV tokamak with local and global gyrokinetic GENE simulations

Complex-Hamiltonian paraxial description of damped geodesic acoustic modes

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