Dr. Toseo Moritaka, National Institute for Fusion Science-Japan

"Development of particle-in-cell gyrokinetic code XGC-S for whole device modeling of Stellarators"

Abstract: We report current status of the development of X-point included Gyrokinetic Code, XGC-S, for whole device modeling of Stellarators. XGC was originally developed for Tokamaks to investigate edge plasma dynamics and core-edge coupling relevant to H-mode transition, divertor heat load, X-point particle loss and so on. These are also important issues however poorly understood in Stellarators. The gyrokinetic approach including finite Larmor radius effect and anisotropic particle motion is effective to investigate roles of stochastic field line structures in the plasma transport.

One major improvement needed for Stellarators is to extend to non-axisymmetric geometries with stochastic regions. Three dimensional VMEC equilibria are employed for the core region and field-alined triangular mesh is generated based on the VMEC magnetic coordinate. The equilibrium magnetic field is re-defined in the cylindrical coordinate and smoothly extends to the outer vacuum field by using virtual casing method. The field-alined mesh is connected to an unstructured triangular mesh generated by field-line tracing in the outer magnetic field. The cylindrical and triangular meshes defined for the entire region are simultaneously used to advance electrostatic field and particle phase.

We present initial results of the application of XGC-S to high-energy particle tracing and collisionless GAM oscillation in Large Helical Device together with basic properties of the generated meshes.

We will also introduce advanced simulation schemes of XGC employed in Tokamak simulations that can be applied for Stellarators in future.