A new hybrid-Lagrangian numerical scheme for gyrokinetic simulation of tokamak edge plasma

Authors: S. Ku, R. Hager, C.S. Chang, J.M. Kwon, and S.E. Parker

Abstract: A new hybrid-Lagrangian δf scheme has been developed that utilizes the phase space grid in addition to the usual marker particles, in order to take advantage of the computational and physical strengths from both sides. The new scheme splits the particle distribution function of a kinetic equation into two parts. Marker particles contain the fast space-time varying, δf part of the distribution function and the coarse-grained phase-space grid contains the slow space-time varying part. The coarse-grained phase-space grid has a low memory-requirement while the marker particles provide scalable computing ability. Weights of the marker particles are determined by a direct weight evolution equation instead of the differential form weight evolution equations that the conventional delta-f schemes use. The particle weight is slowly transferred to the phase space grid, thereby reducing the growth of the particle weights. The non-Lagrangian part of the kinetic equation - e.g., collision operation, ionization, charge exchange, heat-source, radiative cooling, and others - can be operated directly on the phase space grid. Deviation of the particle distribution function on the velocity grid from a Maxwellian distribution function is allowed to be arbitrarily large. The numerical scheme is implemented in the gyrokinetic particle code XGC1, which specializes in simulating the tokamak edge plasma that crosses the magnetic separatrix and is in contact with the material wall.
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Submitted to:  Journal of Computational Physics
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Download PPPL-5212 (pdf 2 MB 19 pp)
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