Abstract
Poloidal asymmetries of the propagation velocity of density fluctuations perpendicular to the magnetic field measured with Doppler reflectometry have been reported in several magnetic confinement plasma devices. Careful analysis of a large variety of different low confinement mode plasma scenarios performed at the ASDEX Upgrade tokamak does not reveal such an asymmetry outside the uncertainties of the evaluation process of the measurement data. The perpendicular velocity is investigated between mid-radius and the plasma edge and follows the poloidal dependence of the E × B drift velocity regardless of the probed turbulence structure size. Compared to measurements of a charge exchange recombination spectroscopy diagnostic this points towards a significantly smaller phase velocity than the E × B drift velocity. The analysis technique is presented in a representative discharge together with a sensitivity study of the impact of density, magneto hydrodynamic equilibrium and diagnostic alignment on the interpretation of the measured Doppler shift using ray tracing and thus on poloidal asymmetries. Three more highly different plasma scenarios with poloidally symmetric velocity profiles are shown.
Highlights
Magnetic confinement fusion power plants will have high energy confinement times, plasma densities and temperatures
This paper reports on recent measurements at the ASDEX Upgrade tokamak (AUG), where the perpendicular propagation velocity of density fluctuations is found to be independent of the poloidal angle apart from the trivial poloidal dependence of the E × B velocity
In order to locate the scattering position of the microwave beam in the plasma ray tracing calculations were carried out. They rely on the density profiles shown in figure 2 measured by a Thomson scattering (TS) diagnostic [23]
Summary
Magnetic confinement fusion power plants will have high energy confinement times, plasma densities and temperatures. These parameters are directly influenced by turbulence which. Plasma turbulence is decorrelated and dissipated by sheared plasma flows. The latter are believed to play a crucial role in the reduction of turbulence and the development of a pedestal in the transition from the low to the high plasma confinement mode [3]. They are an important input parameter for modelling turbulence or transport and consolidated experimental observations are of major interest
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