Analysis and design of fast flow liquid Li divertor for fusion nuclear science facility (FNSF) using coupled plasma boundary and LM MHD/heat transfer codes ^*

Abstract

The SOLPS-ITER code is utilized to analyze the boundary plasma associated with a fast-flow lithium (Li) divertor configuration in the Fusion Nuclear Science Facility (FNSF) tokamak and identify operational regimes with acceptable divertor and core conditions. Plasma transport from the SOLPS-ITER code has been coupled with a liquid metal (LM) MHD/heat transfer code to model a Li open-surface divertor design and assess its impact on the scrape-off-layer (SOL) and core plasma performance. Simulations with only Neon (Ne) impurity seeding have been conducted to evaluate its impact on meeting FNSF design demands for the divertor and upstream plasma parameters. Simulation results indicate that Ne seeding significantly mitigates divertor heat flux but potentially reduces both upstream electron and main ion density due to fuel dilution. The combined application of Ne seeding and deuterium (D2) puffing is required to satisfy the FNSF design requirements on upstream density (1e20) and divertor energy flux ( < 10 MW/m2). D2 puffing plays a role in counteracting upstream density drops and augmenting energy and momentum losses through atomic and molecular processes.

The inlet Li flow velocity is systematically varied across a wide range to identify acceptable flows and corresponding LM surface temperatures. This comprehensive analysis identifies the acceptable Li flow parameters, LM surface temperature, and emitted Li fluxes necessary to meet the major design constraints. The emitted Li fluxes exhibit minimal impact on the main plasma at surface temperatures up to approximately 525^C, corresponding emitted Li fluxes of up to 2e23 atoms/s. Uncertainties in the Li emission processes from the surface are also investigated, primarily influencing Li loss in the lower surface temperature range (525C). Conversely, evaporation predominantly drives the Li loss processes at higher surface temperature ranges (525C), contaminating both the divertor and upstream plasma.

Optimization of lithium vapor box divertor evaporator location on NSTX-U using SOLPS-ITER

“…Sections 3-5 scan the total lithium emission from the evaporator as it assumed to be externally controllable in the vapor box since the evaporator is away from the plasma particle and power flux. Similar flowing liquid metal temperature calculations to those presented in section 6 have been done in other literature [17] by coupling to a flowing liquid metal MHD code. There it was used in tandem with neon gas injection, making lithium evaporation less significant to the overall plasma solution.…”