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 kx, but the oscillation and damping time scales are longer in local representations, particularly for small kx approaching the system size.
Highlights
Control of turbulent transport is a crucial step in the development of fusion energy
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)
Neoclassical transport and flow damping in quasi-symmetric stellarators are more similar to tokamaks than to classical stellarators, we show that the linear zonal flow response for a realistic but almost quasi-symmetric geometry still resembles a classical stellarator
Summary
Control of turbulent transport is a crucial step in the development of fusion energy. This is commonly the case, and the residual is sometimes used as a proxy for the resulting turbulence saturation.16 This is unlikely to be true if the collisionless damping to the residual is slow compared to the rate at which turbulence injects energy into the zonal flow. Calculations in this paper are linear and do not address the transfer of energy between modes, but can examine changes in the collisionless damping of the zonal flow. When the magnetic field is described by a single mode, the collisionless bounce-averaged drift of trapped particles from a flux surface goes to zero, reducing neoclassical transport and flow damping. The zonal flow damping is numerically calculated in flux-tube, flux-surface, and full-volume geometry representations for quasi-symmetric configurations.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
