The dynamics of secondary large-scale structures in electron-temperature-gradient （ETG） turbulence is investigated based on gyrofluid simulations in sheared slab geometry. It is found that structural bifurcation to ...The dynamics of secondary large-scale structures in electron-temperature-gradient （ETG） turbulence is investigated based on gyrofluid simulations in sheared slab geometry. It is found that structural bifurcation to zonal flow dominated or streamer-like states depends on the spectral anisotropy of turbulent ETG fluctuation, which is governed by the magnetic shear. The turbulent electron transport is suppressed by enhanced zonal flows. However, it is still low even if the streamer is formed in ETG turbulence with strong shears. It is shown that the low transport may be related to the secondary excitation of poloidal long-wavelength mode due to the beat wave of the most unstable components or a modulation instability. This large-scale structure with a low frequency and a long wavelength may saturate, or at least contribute to the saturation of ETG fluctuations through a poloidal mode coupling. The result suggests a low fluctuation level in ETG turbulence.展开更多
1 Introduction Much attention has been paid to the anomalous electron transport in magnetic confinement fusion plasmas. Recent renewed interest in this subject is the role of large-scale structures, such as zonal flo...1 Introduction Much attention has been paid to the anomalous electron transport in magnetic confinement fusion plasmas. Recent renewed interest in this subject is the role of large-scale structures, such as zonal flows and streamers, in electron transport. This may partly be stimulated by the exciting achievements on the understanding of ion turbulent transport, which is suppressed to neoclassical transport level by sheared E × B or zonal flows in experiments and theories. Recently, a streamer-like structure is observed in gyrokinetic toroidal ETG turbulence based on a local flux-tube simulation.展开更多
基金supported in part by the National Natural Science Foundation of China(Nos.10135020 and 10575032)
文摘The dynamics of secondary large-scale structures in electron-temperature-gradient （ETG） turbulence is investigated based on gyrofluid simulations in sheared slab geometry. It is found that structural bifurcation to zonal flow dominated or streamer-like states depends on the spectral anisotropy of turbulent ETG fluctuation, which is governed by the magnetic shear. The turbulent electron transport is suppressed by enhanced zonal flows. However, it is still low even if the streamer is formed in ETG turbulence with strong shears. It is shown that the low transport may be related to the secondary excitation of poloidal long-wavelength mode due to the beat wave of the most unstable components or a modulation instability. This large-scale structure with a low frequency and a long wavelength may saturate, or at least contribute to the saturation of ETG fluctuations through a poloidal mode coupling. The result suggests a low fluctuation level in ETG turbulence.
文摘1 Introduction Much attention has been paid to the anomalous electron transport in magnetic confinement fusion plasmas. Recent renewed interest in this subject is the role of large-scale structures, such as zonal flows and streamers, in electron transport. This may partly be stimulated by the exciting achievements on the understanding of ion turbulent transport, which is suppressed to neoclassical transport level by sheared E × B or zonal flows in experiments and theories. Recently, a streamer-like structure is observed in gyrokinetic toroidal ETG turbulence based on a local flux-tube simulation.
