Improving gyrokinetic field solvers toward whole-volume modeling of stellarators

We develop novel numerical schemes for electrostatic field solvers toward the whole-volume gyrokinetic simulation of stellarators. The gyrokinetic Poisson equation should be solved for complicated magnetic fields in the stellarator without assuming nested flux surfaces and toroidal symmetry. The developed schemes enable us to generate suitable unstructured meshes and obtain the solutions within a limited numerical cost for general magnetic field structures. These schemes will be integrated and utilized in X-point Gyrokinetic Code - Stellarator (XGC-S). (author)