Improved linearized model collision operator for the highly collisional regime

Sugama, H.; Matsuoka, Seikichi; Satake, S.; Nunami, M.; Watanabe, Toshiya

doi:10.1063/1.5115440

Cited by 19 publications

(24 citation statements)

References 65 publications

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“…Finally, we remark that the Hermite–Laguerre expansion presented here can be easily applied to other GK collision operators, such as the improved GK Sugama operator (Sugama et al. 2019). Ultimately, it allows for comparisons between collision operator models over a wide range of physical phenomena.…”

Section: Discussionmentioning

confidence: 90%

“…We remark that, because the difference with the Sugama and Coulomb operator is expected to increase at high collisionality, the Sugama operator was recently improved and extended to the regime of high-collisionality in Sugama et al. (2019). In this work, we focus on the original Sugama operator, presented in Sugama et al.…”

Section: Linearized Collision Operator Modelsmentioning

confidence: 95%

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Development of advanced linearized gyrokinetic collision operators using a moment approach

et al. 2021

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The derivation and numerical implementation of a linearized version of the gyrokinetic (GK) Coulomb collision operator (Jorge et al., J. Plasma Phys., vol. 85, 2019, 905850604) and of the widely used linearized GK Sugama collision operator (Sugama et al., Phys. Plasmas, vol. 16, 2009, 112503) is reported. An approach based on a Hermite–Laguerre moment expansion of the perturbed gyrocentre distribution function is used, referred to as gyromoment expansion. This approach allows the considering of arbitrary perpendicular wavenumber and expressing the two linearized GK operators as a linear combination of gyromoments where the expansion coefficients are given by closed analytical expressions that depend on the perpendicular wavenumber and on the temperature and mass ratios of the colliding species. The drift-kinetic (DK) limits of the GK linearized Coulomb and Sugama operators are also obtained. Comparisons between the gyromoment approach and the DK Coulomb and GK Sugama operators in the continuum GK code GENE are reported, focusing on the ion-temperature-gradient instability and zonal flow damping, finding an excellent agreement. It is confirmed that stronger collisional damping of the zonal flow residual by the Sugama GK model compared with the GK linearized Coulomb (Pan et al., Phys. Plasmas, vol. 27, 2020, 042307) persists at higher collisionality. Finally, we show that the numerical efficiency of the gyromoment approach increases with collisionality, a desired property for boundary plasma applications.

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Section: Discussionmentioning

confidence: 90%

Section: Linearized Collision Operator Modelsmentioning

confidence: 95%

Development of advanced linearized gyrokinetic collision operators using a moment approach

et al. 2021

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“…Strictly speaking, however, f a0 is approximated with f aM in the linearised collision operator for the present work. Also, the recent attempts to extend the collision operator to include higher-order terms which can be important for impurity transport (Sugama et al 2019;Calvo et al 2020) are not considered. The equations (2.1)-(2.6) are reduced to the equations for a case without Φ 1 by setting Φ 1 = 0.…”

Section: )mentioning

confidence: 99%

Global calculation of neoclassical impurity transport including the variation of electrostatic potential

et al. 2020

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Recently, the validity range of the approximations commonly used in neoclassical calculation has been reconsidered. One of the primary motivations behind this trend is observation of an impurity hole in LHD (Large Helical Device), i.e. the formation of an extremely hollow density profile of an impurity ion species, such as carbon $\text{C}^{6+}$ , in the plasma core region where a negative radial electric field ( $E_{r}$ ) is expected to exist. Recent studies have shown that the variation of electrostatic potential on the flux surface, $\unicode[STIX]{x1D6F7}_{1}$ , has significant impact on neoclassical impurity transport. Nevertheless, the effect of $\unicode[STIX]{x1D6F7}_{1}$ has been studied with radially local codes and the necessity of global calculation has been suggested. Thus, we have extended a global neoclassical code, FORTEC-3D, to simulate impurity transport in an impurity hole plasma including $\unicode[STIX]{x1D6F7}_{1}$ globally. Independently of the $\unicode[STIX]{x1D6F7}_{1}$ effect, an electron root of the ambipolar condition for the impurity hole plasma has been found by global simulation. Hence, we have considered two different cases, each with a positive (global) and a negative (local) solution of the ambipolar condition, respectively. Our result provides another support that $\unicode[STIX]{x1D6F7}_{1}$ has non-negligible impact on impurity transport. However, for the ion-root case, the radial $\text{C}^{6+}$ flux is driven further inwardly by $\unicode[STIX]{x1D6F7}_{1}$ . For the electron-root case, on the other hand, the radial particle $\text{C}^{6+}$ flux is outwardly enhanced by $\unicode[STIX]{x1D6F7}_{1}$ . These results indicate that how $\unicode[STIX]{x1D6F7}_{1}$ affects the radial particle transport crucially depends on the profile of the ambipolar- $E_{r}$ , which is found to be susceptible to $\unicode[STIX]{x1D6F7}_{1}$ itself and the global effects.

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“…These linear operators were developed for δ f studies [11,12,13] and preserved key properties of the FPO, like conservation (of particles, momentum and energy) and non-decreasing entropy. More recently, improved collision models for gyrokinetics have been formulated and implemented in several codes [14,15,16]. They retained important physics, such as velocity-dependent collisionalities and FLR effects, but are still linearized operators.…”

Section: Introductionmentioning

confidence: 99%

Conservative discontinuous Galerkin scheme of a gyro-averaged Dougherty collision operator

et al. 2020

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A conservative discontinuous Galerkin scheme for a nonlinear Dougherty collision operator in fullf long-wavelength gyrokinetics is presented. Analytically this model operator has the advective-diffusive form of Fokker-Planck operators, it has a non-decreasing entropy functional, and conserves particles, momentum and energy. Discretely these conservative properties are maintained exactly as well, independent of numerical resolution. In this work the phase space discretization is performed using a novel version of the discontinuous Galerkin scheme, carefully constructed using concepts of weak equality and recovery. Discrete time advancement is carried out with an explicit time-stepping algorithm, whose stability limits we explore. The formulation and implementation within the long-wavelength gyrokinetic solver of Gkeyll are validated with relaxation tests, collisional Landau-damping benchmarks and the study of 5D gyrokinetic turbulence on helical, open field lines.

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Improved linearized model collision operator for the highly collisional regime

Cited by 19 publications

References 65 publications

Development of advanced linearized gyrokinetic collision operators using a moment approach

Development of advanced linearized gyrokinetic collision operators using a moment approach

Global calculation of neoclassical impurity transport including the variation of electrostatic potential

Conservative discontinuous Galerkin scheme of a gyro-averaged Dougherty collision operator

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