SOLPS-ITER calculations of lithium vapor box mitigation of q^peak_target = 96 MW/m² in NSTX-U

NSTX-U can provide a valuable test facility for reactor-relevant heat fluxes. Goldston-Eich scaling of the H-mode SOL power width [1,2] for NSTX-U parameters (P_in = 10MW, f^rad=0.3, I_p=2MA, B_T=1T) gives a prediction of q^peak_target ~ 96 MW/m² for extremely low flux expansion geometry. The lithium vapor box seeks to detach the plasma via dense lithium vapor localized near the target through evaporation and condensation [3]. Extensive modeling has been done on a simple lithium evaporation concept, proving its viability in detaching a lower heat flux L-mode discharge at a viable upstream lithium concentration [4]. Here the design of the vapor box is examined for high-power NSTX-U H-modes using a higher degree of divertor closure than previously simulated by SOLPS. Configurations with and without a baffle are compared using upstream lithium concentration, divertor heat flux reduction, and upstream plasma temperature as primary metrics of performance. The heat flux to the target is seen to be reduced to levels that should be acceptable for capillary porous material, ≤ 15 MW/m². The next set of studies will examine the role of deuterium gas puffing in reducing upstream lithium concentration from the values of ~5% currently observed.

[1] R.J Goldston 2012 Nucl. Fusion 52 013009

[2] T. Eich et al. 2013 Nucl. Fusion 53 093031

[3] R.J Goldston et al. 2016 Phys. Scr. 2016 014017

[4] E.D Emdee et al. 2021 Nuclear Materials and Energy 27 101004