Authors: C-S. Chang, S. Ku
Abstract: In order to save the computing time or to
fit the simulation size into a limited computing hardware in
a gyrokinetic turbulence simulation of a tokamak plasma, a
toroidal wedge simulation may be utilized in which only a partial
toroidal section is modeled with a periodic boundary condition
in the toroidal direction. The most scvere restriction in
the wedge simulation is expected to be in the longest wavelength
turbulence, i.e., ion temperature gradient (ITG) driven
turbulence. The global full-f gyrokinetic code XGC 1 is used to
compare the transport and turbulence properties from a toroidal
wedge simulation against the full torus simulation in an ITG
unstable plasma in a model toroidal geometry. It is found
that (1) the convergence study in the wedge number needs to be
conducted all the way down to the full torus in order to avoid a
false convergence, (2) a reasonably accurate simulation can be
performed if the correct wedge number N can be identified, (3) the
validity of a wedge simulation may be checked by performing a
wave-number spectral analysis of the turbulence amplitude jdUj
and assuring that the variation of dU between the discrete kh values is less than
25% compared to the peak jdUj, and (4) a frequency
spectrum may not be used for the validity check of a wedge
simulation.
Submitted to: Physics of Plasmas
_________________________________________________________________________________________________
Download PPPL-5354
1.8 MB (11 pp)
_________________________________________________________________________________________________