A fully non-linear multi-species Fokker-Planck-Landau collision operator for simulation of fusion plasma

Authors:  Robert Hager, E.S. Yoon, S. Ku, E.F. D'Azevedo, P.H. Worley, C.S. Chang

Abstract:  Fusion edge plasmas can be far from thermal equilibrium and require the use of a non-linear collision operator for accurate numerical simulations. In this article, the non-linear single-species Fokker-Planck-Landau collision operator developed by Yoon and Chang [Phys. Plasmas 21, 032503 (2014)] is generalized to include multiple particle species. The nite volume dis-cretization used in this work naturally yields exact conservation of mass, momentum, and energy. The implementation of this new non-linear Fokker-Planck-Landau operator in the gyrokinetic particle-in-cell codes XGC1 and XGCa is described and results of a verication study are discussed. Finally, the numerical techniques that make our non-linear collision operator viable on high-performance computing systems are described, including special-ized load balancing algorithms and nested OpenMP parallelization. The collision operator's good weak and strong scaling behavior are shown.
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