Gyrokinetic simulations are fundamental to understanding and predicting turbulent transport in magnetically confined fusion plasmas. Previous simulations have used model collision operators with approximate field-particle terms of unknown accuracy and/or have neglected collisional finite Larmor radius (FLR) effects. We have implemented the linearized Fokker–Planck collision operator with exact field-particle terms and full FLR effects in a gyrokinetic code (GENE). The new operator, referred to as “exact” in this paper, allows the accuracy of model collision operators to be assessed. The conservative Landau form is implemented because its symmetry underlies the conservation laws and the H-theorem, and enables numerical methods to preserve this conservation, independent of resolution. The implementation utilizes the finite-volume method recently employed to discretize the Sugama collision model in GENE, allowing direct comparison between the two operators. Results show that the Sugama model appears accurate for the growth rates of trapped electron modes (TEMs) driven only by density gradients, but appreciably underestimates the growth rates as the collisionality and electron temperature gradient increase. The TEM turbulent fluxes near the nonlinear threshold using the exact operator are similar to the Sugama model for the case, but substantially larger than the Sugama model for the case. The FLR effects reduce the growth rates increasingly with wavenumber, deepening a “valley” at the intermediate binormal wavenumber as the unstable mode extends from the TEM regime to the electron temperature gradient instability regime. Application to the Hinton–Rosenbluth problem shows that zonal flows decay faster as the radial wavenumber increases and the exact operator yields weaker decay rates.
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April 2020
Research Article|
April 16 2020
First implementation of gyrokinetic exact linearized Landau collision operator and comparison with models
Special Collection:
Papers from the 61st Annual Meeting of the APS Division of Plasma Physics
Qingjiang Pan;
1
Plasma Science and Fusion Center, Massachusetts Institute of Technology
, Cambridge, Massachusetts 02139, USA
b)Author to whom correspondence should be addressed: [email protected]
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Darin R. Ernst;
Darin R. Ernst
c)
1
Plasma Science and Fusion Center, Massachusetts Institute of Technology
, Cambridge, Massachusetts 02139, USA
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Paul Crandall
Paul Crandall
2
Department of Physics and Astronomy, University of California
, Los Angeles, California 90095, USA
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a)
Invited speaker.
b)Author to whom correspondence should be addressed: [email protected]
c)
Electronic email: [email protected]
Note: This paper is part of the Special Collection: Papers from the 61st Annual Meeting of the APS Division of Plasma Physics.
Note: Paper GI2 6, Bull. Am. Phys. Soc. 64 (2019).
Phys. Plasmas 27, 042307 (2020)
Article history
Received:
December 23 2019
Accepted:
March 26 2020
Citation
Qingjiang Pan, Darin R. Ernst, Paul Crandall; First implementation of gyrokinetic exact linearized Landau collision operator and comparison with models. Phys. Plasmas 1 April 2020; 27 (4): 042307. https://doi.org/10.1063/1.5143374
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