Flux-Coordinate-Independent Extension to BOUT++/HERMES-3

Realizing viable fusion power plants (FPPs) demands whole‑device modeling, integrating high‑fidelity plasma simulations with engineering systems and design capabilities. Among the most pressing challenges are accurate predictions of heat and particle exhaust in the divertor region and self‑consistent plasma–neutral and plasma–wall interactions in the edge and scrape‑off layer. The BOUT++/Hermes-3 [1] fluid framework is extended here with a flux‑coordinate‑independent (FCI) discretization in cylindrical coordinates [2], enabling full‑device transport and turbulence studies from the core to first wall. The FCI approach offers various advantages, namely the ability to handle the complicated magnetic topologies and divertor geometries which are characteristic of edge plasmas. Futhermore, the new FCI grids can easily be extended to magnetic mirror and stellarator configurations. Plasma flow operators are implemented using a novel anti‑symmetric approach, improving spectral fidelity and energy conservation versus conventional finite‑difference methods [3]. The FCI‑based model will be used to study edge transport in stochastic fields and divertor regions, offering predictive insight into exhaust management for next‑generation FPPs.

[1] B. Dudson et al Comp. Phys. Comm. 296 108991 (2024)

[2] F. Hariri and M. Ottaviani Comp. Phys. Comm. 184 2419-2429 (2013)

[3] F. D. Halpern et al Comp. Phys. Comm. 315 109696 (2025)