Applicability of different geometry approaches to simulations of turbulence in highly sheared magnetic fields

Abstract

For more than a decade, Eulerian simulations of plasma turbulence have been using coordinate systems aligned to the background magnetic field in order to exploit the elongated structure of the turbulent eddies. Here, two possible setups of such field-aligned coordinate systems are studied with regard to their behavior under more extreme conditions such as tokamak edge or stellarator geometries where large global and/or local shear are encountered. Turbulence codes employing a Fourier expansion are shown to yield correct solutions also for large shear values, given that the radial resolution chosen is large enough. Codes which compute the radial direction in real space, on the other hand, can benefit from the implementation of the shifted metric approach which may save resolution in the case of large shear.