Field-aligned semi-Lagrangian methods for turbulence simulations of strongly magnetized plasmas

Summary form only given. Plasma turbulence in strongly magnetized plasmas is characterized by long wavelengths along the magnetic field, of the order of the system size, and by short perpendicular wavelengths, of the order of the ion gyro-radius. This strong anisotropy suggests the use of field-aligned coordinates in order to drastically reduce the number of grid points along a certain direction (usually parallel to the field).Traditionally, field-aligned discretizations are derived from predefined flux coordinates; in practice, this limits their use to simple geometries and magnetic field configurations. Recently [1] the use of more general field-aligned coordinates was proposed, which do not depend on flux surface variables. This approach allows for increased flexibility, and it is suitable to modeling X-point magnetic field configurations. Therefore, it is a perfect candidate for the global simulation of modern magnetic fusion reactors like ITER. Here we describe the implementation of this new field-aligned strategy within the semi-Lagrangian library SeLaLib [2], for solution of the gyrokinetic equations in 5D phase-space [3]. Our aim is to simulate turbulence in Tokamak and Stellarator reactors. We present verification of our code against analytical solutions for a periodic cylinder, as well as preliminary results in axially-symmetric toroidal geometry (Tokamak). Finally, we discuss the future extension of the code to more general toroidal geometries (Stellarator).