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.
| Original language | English |
|---|---|
| Article number | 042503 |
| Number of pages | 11 |
| Journal | Physics of Plasmas |
| Volume | 28 |
| Issue number | 4 |
| DOIs | |
| Publication status | Published - 1 Apr 2021 |
Bibliographical note
Funding Information:The authors would like to acknowledge helpful discussions with C.C. Hegna. This research has been supported by U.S. DOE Grant Nos. DE-FG02-93ER54222 and DE-FG02-04ER54742 and used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231. This work has been partially funded by the Ministerio de Economía y Competitividad of Spain under Project Nos. ENE2015-70142-P and PGC2018-095307-B-I00. The authors acknowledge the computer resources at Mare Nostrum IV and the technical support provided by the Barcelona Supercomputing Center and the CIEMAT computing center. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom Research and Training Programme 2014–2018 and 2019–2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.