Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators

Abstract

The linear collisionless damping of zonal flows is calculated for quasi-symmetric stellarator equilibria in flux-tube, flux-surface, and full-volume geometry. Equilibria are studied from the quasi-helical symmetry configuration of the Helically Symmetric eXperiment (HSX), a broken symmetry configuration of HSX, and the quasi-axial symmetry geometry of the National Compact Stellarator eXperiment (NCSX). Zonal flow oscillations and long-time damping affect the zonal flow evolution, and the zonal flow residual goes to zero for small radial wavenumber. The oscillation frequency and damping rate depend on the bounce-averaged radial particle drift in accordance with theory. While each flux tube on a flux surface is unique, several different flux tubes in HSX or NCSX can reproduce the zonal flow damping from a flux-surface calculation given an adequate parallel extent. The flux-surface or flux-tube calculations can accurately reproduce the full-volume long-time residual for moderate $k_x$, but the oscillation and damping time scales are longer in local representations, particularly for small $k_x$ approaching the system size.

arXiv commentThe following article has been accepted by Physics of Plasmas. After it is published, it will be found at https://aip.scitation.org/journal/php. 33 pages, 18 figures

References in corpus (7)

• Residual zonal flows in tokamaks and stellarators at arbitrary wavelengths
• The Parallel Boundary Condition for Turbulence Simulations in Low Magnetic Shear Devices
• Nonlinear gyrokinetic PIC simulations in stellarators with the code EUTERPE
• Distinct turbulence saturation regimes in stellarators
• Semianalytical calculation of the zonal-flow oscillation frequency in stellarators
• Ion temperature gradient turbulence in helical and axisymmetric RFP plasmas
• Oscillatory relaxation of zonal flows in a multi-species stellarator plasma

Cited by in corpus (5)

• Electrostatic gyrokinetic simulations in Wendelstein 7-X geometry: benchmark between the codes stella and GENE
• Instabilities and turbulence in stellarators from the perspective of global codes
• Collisionless zonal-flow dynamics in quasisymmetric stellarators
• Global linear drift-wave eigenmode structures on flux surfaces in stellarators: ion temperature gradient mode
• Gyrokinetic simulations in stellarators using different computational domains