Experimental study reveals direct measurements of radial electric field fluctuations across tokamak plasma confinement regimes, highlighting turbulence regulation by zonal flows.
Zonal flows (ZFs) and associated geodesic oscillations are turbulence-generated time-varying E r × B T rigid poloidal plasma flows with finite radial extent. They are of major interest for tokamak confinement since they are thought to moderate drift-wave turbulence and hence edge transport. However, detection of ZFs (believed to be driven by Reynolds stress) and Geodesic acoustic modes (GAMs) (linked with poloidal pressure asymmetries) is challenging since they appear predominantly as low frequency (few kilohertz) potential or radial electric field E r fluctuations. Presented here are measurements of GAM/ZF properties in ohmic, L-mode and H-mode ASDEX Upgrade tokamak discharges using a new Doppler reflectometry technique to measure E r fluctuations directly.
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Conway et al. (2005) studied this question.