Multiblock discontinuous Galerkin continuum gyrokinetics in Gkeyll

Magnetized laboratory plasmas are housed in a variety of vessels whose shapes cannot all be modeled fairly by a single coordinate mapping in (fluid or kinetic) simulations. For example, in a simple linear cylindrical device, the intuitive cylindrical mapping can introduce a coordinate singularity at the axis or produce cells so small in that region that the stable time step becomes impractically small. To this end we explore the use of multiple field-aligned coordinate mappings in distinct domains that are connected in a single simulation to cover a geometry as simple as a cylindrical plasma or as complex as a diverted tokamak. This work explores this approach in the context of continuum gyrokinetic simulations with discontinuous Galerkin methods in the Gkeyll computational plasma physics framework. We describe the physical requirements, the numerics developed to preserve physical properties, and the verification exercises done to guarantee proper formulation and implementation.