GITRm: A 3D Unstructured Mesh-based Particle Tracking Code for Global Impurity Transport in Fusion Devices*

GITRm is a 3D unstructured mesh-based Monte Carlo particle (neutral atom and ion) tracking code for global impurity transport in fusion-relevant devices. It is designed to target complex wall geometries, including non-axisymmetric local features such as bumpers, probes, etc., and account for their interactions with the plasma. It is capable of resolving the gyro-motion of impurity particles in 3D. It is built on the PUMIPic infrastructure that is designed to be performant on multi-GPU computers. It uses strongly graded and anisotropic elements to efficiently and accurately represent the plasma fields from multiple sources, especially in a 3D/volumetric fashion. The sheath electric field can be calculated analytically or obtained from a sheath simulator. For example, procedures have been developed in GITRm to integrate a sheath mesh on which an electric field has been calculated from the particle-in-cell based kinetic code hPIC2. Furthermore, the capabilities of GITRm have been extended to simulate multiple impurity species simultaneously and their interactions with different material surfaces including mixed surfaces. Results of the impurity transport simulations will be shown for multiple cases such as the ITER and DIII-D geometries including local features.