Progress with the 5D continuum gyrokinetic code COGENT: moving toward an edge turbulence code

The presence of a strong magnetic shear in the edge of a diverted tokamak provides a significant challenge for continuum numerical modelling of edge microturbulence, which generates highly-anisotropic perturbations aligned with the magnetic field. In this work we propose a finite-volume mapped multiblock approach to the discretization of a gyrokinetic system of equations for plasma species and electrostatic fields that can accommodate large values of a magnetic shear and can handle an X-point geometry. In this approach, the toroidal direction is divided into blocks, such that within each block cells are field-aligned and a non-matching (non-conformal) grid interface is allowed at block boundaries. The toroidal angle is playing the role of the “coarse” field-aligned coordinate, whereas the poloidal cross-section, comprised of the radial and poloidal directions, is finely gridded to resolve short-scale perpendicular turbulence structures and to support accurate re-mapping (interpolation) at block boundaries. The method is implemented in the gyrokinetic code COGENT and the results of initial simulations in simplified geometries are presented.