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Turbulent generation of poloidal asymmetries of the electric potential in a tokamak

Abstract : Poloidal asymmetries of the E × B plasma flow are known to play a role in neoclassical transport. One obvious reason is that an asymmetrical potential can produce a flux. Also the associated distribution function may correlate with the magnetic drift velocity to enhance the neoclassical flux. Finally, poloidal variation of the electric potential can produce poloidal asymmetries of the density of an impurity, which in turn may enhance its neoclassical flux. According to conventional neoclassical theory, the level of poloidal asymmetry of the electric potential is expected to be very small. Conversely, poloidal flow asymmetries can be driven by small scale turbulence via non linear coupling, and therefore change this result. In the present work, a general framework for the generation of axisymmetric structures of potential by turbulence is presented. Zonal flows, geodesic acoustic modes and convective cells are described by a single model. This is done by solving the gyrokinetic equation coupled to the quasi-neutrality equation. This calculation provides a predictive calculation of the frequency spectrum of flows. It also shows that the dominant mechanism comes from zonal flow compression at intermediate frequencies, while ballooning of the turbulence Reynolds stress appears to be the main drive at low frequency.
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Submitted on : Friday, June 29, 2018 - 4:45:22 PM
Last modification on : Tuesday, April 19, 2022 - 3:54:02 PM
Long-term archiving on: : Thursday, September 27, 2018 - 9:21:41 AM

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Peter Donnel, X. Garbet, Y. Sarazin, Y. Asahi, F Wilczynski, et al.. Turbulent generation of poloidal asymmetries of the electric potential in a tokamak. Plasma Physics and Controlled Fusion, IOP Publishing, In press. ⟨hal-01826705⟩

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