Modelling of electrostatic <scp>ion‐scale</scp> turbulence in divertor tokamaks with the gyrokinetic code <scp>COGENT</scp>

We present a study of the linear properties of the ion-temperature gradient (ITG) modes with collisions modelled for the first time by the linearized gyrokinetic (GK) Coulomb collision operator (Frei et al., J. Plasma Phys., vol. 87, issue 5, 2021, 905870501) in the local limit. The study is based on a Hermite–Laguerre polynomial expansion of the perturbed ion distribution function applied to the linearized GK Boltzmann equation, yielding a hierarchy of coupled equations for the expansion coefficients, referred to as gyromoments. We explore the collisionless and high-collisional limits of the gyromoment hierarchy analytically. Parameter scans revealing the dependence of the ITG growth rate on the collisionality modelled using the GK Coulomb operator are reported, showing strong damping at small scales as the collisionality increases and, therefore, the need for a steeper gradient for the ITG onset at high collisionality to overcome the finite Larmor radius (FLR) collisional stabilization. The predictions on the ITG growth rate by the GK Coulomb operator are compared with other collision operator models, such as the Sugama, the Dougherty, as well as the momentum-conserving pitch-angle scattering and the Hirshman–Sigmar–Clarke collision operators derived for the first time in terms of gyromoments. The importance of FLR terms in the collision operators is pointed out by the appearance of a short wavelength ITG branch when collisional FLR terms are neglected, this branch being completely suppressed by FLR collisional effects. Energy diffusion is shown to be important at high collisionality and at small scale lengths. Among the GK collision operators considered in this work, the GK Sugama collision operator yields, in general, the smallest deviation compared with the GK Coulomb collision operator, while the largest deviations are found with the GK Dougherty operator. Convergence studies of the gyromoment method are reported and show that the drifts associated with the gradient and curvature of the magnetic field increase the required number of gyromoments at low collisionality. Nevertheless, the low number of gyromoments necessary for convergence at high collisionality constitutes an attractive numerical and analytical feature of the gyromoment approach to study the plasma dynamics in the boundary of fusion devices.

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“…the transition from resistive ballooning to ITG driven turbulence regime in the boundary region (Zeiler et al. 1998; Dorf & Dorr 2022).…”

Section: Introductionmentioning

confidence: 99%

“…For instance, the collisionality dependence of the ITG mode is important in the prediction of, e.g. the transition from resistive ballooning to ITG driven turbulence regime in the boundary region (Zeiler et al 1998;Dorf & Dorr 2022).…”

Section: Introductionmentioning

confidence: 99%

Local gyrokinetic collisional theory of the ion-temperature gradient mode

2022

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Development of an implicit electromagnetic capability for a hybrid gyrokinetic ion‐fluid electron model

Dorf,

Dorr,

Ghosh

2024

Contrib. Plasma Phys

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We report on the development and implementation of a hybrid kinetic ion–fluid electron model for electromagnetic COGENT simulations of edge plasmas. COGENT is a finite‐volume gyrokinetic code that employs a locally field‐aligned coordinate system combined with a mapped multi‐block grid technology to handle strongly anisotropic edge plasma turbulence. The simulation model involves the long‐wavelength limit of the ion gyrokinetic equation coupled to the vorticity and Ohm's law equations for the electromagnetic field perturbations. In order to handle the fast Alfvén wave time scales, an implicit‐explicit time integration approach with a physics‐based preconditioner is used. The model is successfully applied to the simulations of ion‐scale resistive‐drift ballooning turbulence in a toroidal annulus geometry. Substantial speed‐up over a fully explicit time integration approach is observed.

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Modelling of electrostatic ion‐scale turbulence in divertor tokamaks with the gyrokinetic code COGENT

Cited by 2 publications

References 15 publications

Local gyrokinetic collisional theory of the ion-temperature gradient mode

Local gyrokinetic collisional theory of the ion-temperature gradient mode

Development of an implicit electromagnetic capability for a hybrid gyrokinetic ion‐fluid electron model

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