Testing multispecies MHD algorithms within the accelerator-enabled NIMROD code

Multispecies MHD simulation is critical to fusion-energy applications such as core-edge integration with a radiating detached divertor; disruption mitigation through impurity injection; and burning-plasma physics with multiple fuel species and fusion by-products. Hierarchical models for multicomponent MHD that include closures for a diffusion velocity or evolving a momentum equation for each species are described. The NIMROD code uses a mixed implicit, semi-implicit leapfrog algorithm for single- and two-fluid (electrons and a single ion species) simulations. A semi-implicit operator in the momentum equation is essential for numerical stability for the single and two-fluid models. Approaches to generalize the semi-implicit operator for multiple momentum equations are tested. These capabilities are implemented within a version of the NIMROD MHD code that incorporates device accelerated computing through OpenACC and abstract types as enabled by modern Fortran.