Stellarator Boundary Simulations with BSTING

We present recent advancements in the BSTING model for stellarator boundary simulations, developed as part of the SciDAC-5 HifiStell Project. Originally implemented in Hermes-2, the BSTING model has now been successfully migrated to the more flexible Hermes-3 framework [1], resulting in enhanced robustness, modularity, and expanded physics capabilities. Notable improvements include the adoption of conservative finite-difference methods and improved parallelism, leading to more accurate and faster simulations. The transport model evolves plasma density, electron and ion pressures, and ion momentum with prescribed effective diffusion coefficients, closely mimicking the EMC3 transport model. Meanwhile, the turbulence model self-consistently resolve small-scale turbulent fluctuations. Recent efforts have extended turbulence simulations to include full electron and ion temperature evolution, as well as the incorporation of neutral fluid dynamics to simulate high-recycling regimes. Both transport and turbulence simulations have been performed for W7-X and W7-AS stellarator configurations, demonstrating the versatility of the code. The updated BSTING model now enables the study of drift effects, a long-standing need in the community, and supports code coupling via the ADIOS interface.

[1] Dudson et al., CPC 296 108991 2024