Abstract
Global gyrokinetic particle simulations of electrostatic ion temperature gradient (ITG) instability show that the most unstable eigenmode is localized to some magnetic fieldlines or discrete locations on the poloidal plane in the Wendelstein 7-X (W7-X) stellarator due to its mirror-like magnetic fields, which vary strongly in the toroidal direction and induce coupling of more toroidal harmonics (n) to form the linear eigenmode than in the Large Helical Device (LHD) stellarator. Nonlinear electrostatic simulation results show that self-generated zonal flows are the dominant saturation mechanism for the ITG instabilities in both the LHD and W7-X. Furthermore, radial widths of the fluctuation intensity in both the LHD and W7-X are significantly broadened from the linear phase to the nonlinear phase due to turbulence spreading. Finally, nonlinear spectra in the W7-X are dominated by low-n harmonics, which can be generated both by nonlinear toroidal coupling of high-n harmonics and by linear toroidal coupling with large amplitude zonal flows due to the 3D equilibrium magnetic fields.
| Original language | English |
|---|---|
| Article number | 082305 |
| Journal | Physics of Plasmas |
| Volume | 27 |
| Issue number | 8 |
| DOIs | |
| State | Published - Aug 1 2020 |
Funding
The authors would like to thank J. Riemann and R. Kleiber for performing EUTERPE simulations in a careful benchmark and for providing EUTERPE results including the frequency, growth rate, and mode structure in Fig. 5. We acknowledge technical support by the GTC team. This work was supported by the China National Magnetic Confinement Fusion Science Program (Grant No. 2018YFE0304100); the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research and Office of Fusion Energy Sciences, Scientific Discovery through Advanced Computing (SciDAC) program under Award Number DE-SC0018270 (SciDAC ISEP Center); and the China Scholarship Council (Grant No. 201806010067). This work used the resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory (DOE Contract No. DE-AC05–00OR22725) and the National Energy Research Scientific Computing Center (DOE Contract No. DE-AC02–05CH11231). The authors would like to thank J. Riemann and R. Kleiber for performing EUTERPE simulations in a careful benchmark and for providing EUTERPE results including the frequency, growth rate, and mode structure in Fig. 5. We acknowledge technical support by the GTC team. This work was supported by the China National Magnetic Confinement Fusion Science Program (Grant No. 2018YFE0304100); the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research and Office of Fusion Energy Sciences, Scientific Discovery through Advanced Computing (SciDAC) program under Award Number DE-SC0018270 (SciDAC ISEP Center); and the China Scholarship Council (Grant No. 201806010067). This work used the resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory (DOE Contract No. DE-AC05-00OR22725) and the National Energy Research Scientific Computing Center (DOE Contract No. DE-AC02-05CH11231).