Analytic guiding center formulas for bounce-transit motion in a concentric circular, finite inverse aspect ratio tokamak geometry

Stephens, C. D.; Garbet, X.; Jenko, F.

doi:10.1063/5.0004811

Cited by 3 publications

(2 citation statements)

References 36 publications

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“…Such hamiltonian formalism was used in [22,23] to recover the expression for the Rosenbluth-Hinton residual ZF [24] in axisymmetric tokamaks. Formulas for trapped-particle and passing particle guiding-center orbits were obtained in terms of the Jacobi elliptic functions in [25] or were generalized for finite inverse aspect ration in [26]. In general, such a scale separation is not always valid for the transit motion (e.g.…”

Section: Physical Modelmentioning

confidence: 99%

Low-frequency turbulence suppression by amplification of synchronized zonal flow with energetic particle driven modes

Ghizzo,

Del Sarto

2023

Nucl. Fusion

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We investigate the suppression of the turbulent transport associatedto the emergence of spontaneous internal transport barriers, due tothe combined collective effects played by trapped electrons and energeticpassing ions. Numerical experiments performed with a ``particle mode''model based on a double gyro-average over the fast cyclotron phaseand over the bounce (or transit) phases are used to show the roleplayed by energetic particles in the suppression of the ion-temperature-gradientdriven turbulence. We show this occur via phase locking in a Kuramoto-typesynchronization process.

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Section: Physical Modelmentioning

confidence: 99%

Low-frequency turbulence suppression by amplification of synchronized zonal flow with energetic particle driven modes

Ghizzo,

Del Sarto

2023

Nucl. Fusion

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“…Here, we neglect excursions from the field line due to various guiding centre drifts by holding constant. For an extended treatment of bounce-transit motion, see the works of Brizard (2011) and Stephens, Garbet & Jenko (2020).…”

Section: Action-angle Variablesmentioning

confidence: 99%

Quasilinear gyrokinetic theory: a derivation of QuaLiKiz

et al. 2021

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In order to predict and analyse turbulent transport in tokamaks, it is important to model transport that arises from microinstabilities. For this task, quasilinear codes have been developed that seek to calculate particle, angular momentum and heat fluxes, both quickly and accurately. In this tutorial, we present a derivation of one such code known as QuaLiKiz, a quasilinear gyrokinetic transport code. The goal of this derivation is to provide a self-contained and complete description of the underlying physics and mathematics of QuaLiKiz from first principles. This work serves both as a comprehensive overview of QuaLiKiz specifically as well as an illustration for deriving quasilinear models in general.

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Quasilinear modelling of collisional trapped electron modes

Stephens,

Citrin,

van de Plassche

et al. 2024

J. Plasma Phys.

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The simplification of collision operators is necessary for quasilinear turbulence modelling used with integrated modelling frameworks, such as the gyrokinetic code QuaLiKiz. The treatment of collisions greatly impacts the accuracy of trapped electron mode (TEM) modelling, which is necessary to predict the electron heat flux and the balance between inward and outward particle fluxes. In particular, accurate particle flux predictions are necessary to successfully model density peaking in the tokamak core. We explored two ways of improving collisional TEM model reduction for tokamak core plasmas. First, we carried out linear GENE simulations to study the complex interplay between collisions and trapped electrons. We then used these simulations to define an effective trapped fraction to characterize the collisional TEM based on two key parameters, the local inverse-aspect ratio $\epsilon$ and the collisionality $\nu ^\ast$ . One aspect missing from analytical TEM research is that the collisional frequency and the bounce-transit frequency are both velocity dependent; this effective trapped fraction takes both into account. In doing so, we determined that two parameters are not enough to model the collisional TEM, as an additional third free parameter was necessary. We determined that this model, as currently formulated, is not suitable for integrated modelling purposes. Second, we directly improved QuaLiKiz's Krook operator, which relies on two free parameters. We determined that these parameters required adjustments against higher-fidelity collisional models. In order to improve density profile predictions when paired with integrated models, we refined the Krook operator by using GENE simulations as a higher-fidelity point of comparison. We then demonstrate strong improvement of density peaking predictions of QuaLiKiz within the integrated modelling framework JETTO.

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Analytic guiding center formulas for bounce-transit motion in a concentric circular, finite inverse aspect ratio tokamak geometry

Cited by 3 publications

References 36 publications

Low-frequency turbulence suppression by amplification of synchronized zonal flow with energetic particle driven modes

Low-frequency turbulence suppression by amplification of synchronized zonal flow with energetic particle driven modes

Quasilinear gyrokinetic theory: a derivation of QuaLiKiz

Quasilinear modelling of collisional trapped electron modes

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