Magnetic mesh generation and field line reconstruction for scrape-off layer and divertor modeling in stellarators

The design of divertor targets and baffles for optimal heat and particle exhaust from magnetically confined fusion plasmas requires a combination of fast, low-fidelity models (such as EMC3-lite [1]) for scoping studies and high-fidelity ones (such as EMC3-EIRENE [2]) for verification. Both of those approaches benefit from a magnetic flux tube mesh for fast interpolation and mapping of field line segments [3]. A new mesh generator for unstructured quadrilateral flux tubes with adaptive refinement is presented and integrated into FLARE [4]. For HSX with an extended first wall, it is found that several layers of flux tubes can span the entire half field period before splitting is required. This is an advantage over the traditional setup of the EMC3-EIRENE mesh where careful construction of several sub-domains is required already for the much tighter present first wall. The divide and conquer paradigm with unstructured mesh layout offers a powerful alternative for integration into optimization workflows. Further examples for W7-X and CTH are presented.