Speaker
Description
We present the benchmarking of one-dimensional (1D) simulations comparing a newly developed 1D exhaust code RMK_REX [1] with the modelling suite SOLPS-ITER [2]. RMK_REX is developed in the ReMKiT1D framework [3] for fluid-kinetic and collisional-radiative modelling, with the aim of simulating detached plasmas with non-local electron effects. The benchmark serves to calibrate RMK_REX to SOLPS-ITER as these features are developed, using grids and equilibria from the latter to initialise the former. Boundaries in SOLPS-ITER are configured to mimic elements of the 1D treatment including the neutral recycling and the inherent absence of side walls.
Three cases are examined in a linearly expanding flux tube geometry: a plasma-only case, and two plasma-atom cases without and with a cross-field pressure diffusion contribution to the 1D parallel neutral transport. The plasma-only case gives very close agreement, differing only slightly at the downstream boundary. In the plasma-atom case without the cross-field approximation, there are qualitative similarities in electron density, temperature and energy flux, however the target plasma is hotter and less dense, and energy content is overestimated compared to the SOLPS-ITER data. Introducing the cross-field approximation to neutral transport improves agreement in the density and temperature profiles, while underestimating ion and neutral energies compared to SOLPS-ITER. The neutral pressure downstream of the front is found to be much more sensitive to the energetic efficiency with which neutrals reflect from side walls than the target boundary condition itself. Results from this benchmark will help identify improvements and limitations of the 1D reduction of neutral transport as a step towards more complex time-dependent simulations of the detached exhaust.
Finally, future work seeks to incorporate kinetic electron transport with flux expansion. Kinetics alone will introduce deviations from the classical fluid transport coefficients [4], interactions with neutrals [5] and the boundary fluxes [6]. These deviations are likely to be significant for energetic transients in current experiments like MAST Upgrade, or during steady state in plant scale devices.
[1] Leigh, Moulton and Mijin (2026); 27th International Conference on Plasma Surface Interactions, Regensburg, Germany. Submitted to J. Nuclear Materials and Energy.
[2] Wiesen et al 2015 Journal of Nuclear Materials 463 480–484
[3] Mijin et al 2024 Comp. Phys. Comms 300 (2024) 109195
[4] Power et al 2021 Eur. Phys. J. Plus, 136
[5] Chankin et al 2018 Plasma Phys. Control. Fusion 60
[6] Mijin et al 2020 Plasma Phys. Control. Fusion 62 095004