A GPU-Accelerated 3D Unstructured Mesh Based Particle Tracking Code for Multi-Species Impurity Transport Simulation in Fusion Tokamaks

This paper presents the multi-species global impurity transport capability developed in a GPU-accelerated fully 3D unstructured mesh-based code, GITRm, to simultaneously track multiple impurity species and handle interactions of these impurities with mixed-material surfaces. Different computational approaches to model particle-surface interaction or surface response have been developed and compared. Sheath electric field is taken into account by employing a fast distance-to-boundary calculation, which is carried out in parallel on distributed or partitioned meshes on multiple GPUs without the need for any inter-process communication during the simulation. Several example cases, including two for the DIII-D tokamak, that is, one with the SAS-V divertor and the other with the collector probes, are used to demonstrate the utility of the current multi-species capability. For the DIII-D probe case, the capability of GITRm to resolve the spatial distribution of particles in localized regions, such as diagnostic probes, within non-axisymmetric tokamak geometries is demonstrated. These simulations involve up to 320 million particles and utilize up to 48 GPUs.