Speaker
Sanket Gadgil
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1093.pdf
Investigation of zonal flow stability using spatial averaging
S. Gadgil1, B. Hnat1, G. Rowlands1
1 University of Warwick, United Kingdom
Zonal flows are of great interest inside magnetically-confined plasmas as their
interaction with turbulence may in principle be used to control plasma confinement
via processes such as shearing of turbulent eddies due to the alternating nature of the
velocities of the zonal flows. Zonal flows are structures with a poloidal wavenumber
of zero and a larger radial wavenumber but with plasma flow in the poloidal direction.
The growth of zonal flows from drift modes has been extensively studied and non-
linear processes are found to be the driving forces, chiefly 4-wave interactions. The
linear decay of zonal flows can be attributed to energy transfer to compressible
poloidal oscillations(GAMs) via Landau damping and the non-linear decay can be
attributed to a tertiary Kelvin-Helmholtz instability. However, building upon previous
work, the linear stability of zonal flows was re-examined using a spatial averaging
technique. In particular the spatial averaging was applied to the dispersion relation
obtained from the linearised Extended Hasegawa-Wakatani equations. The spatially
independent dispersion relation was solved to yield linear growth rates for a small
drift wave perturbation against a zonal flow background. The growth rates come from
resonance terms which suggests Landau-damping of zonal flows and transfer of
energy to drift waves. The growth rates and energy predictions were compared to
measurements from a simulation and found to match reasonably well under a certain
range of parameters.
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