Study of lithium vapor flow in a detached divertor using DSMC code

Emdee, Eric; Goldston, Robert James; Schwartz, Jacob; Rensink, M.E.; Rognlien, T. D.

doi:10.1016/j.nme.2019.01.032

Cited by 11 publications

(14 citation statements)

References 6 publications

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“…Furthermore, at surface temperatures below 400 C hydrogenic species are anticipated to be pumped, while if the condensing surfaces are maintained at 400 C or above, hydrogenic species are not likely to be dissolved in the lithium, providing flexibility in particle handling. In this paper we extend previous analyses [2,3] to explore lithium vapor localization and detachment stability in a simplified configuration without baffles.…”

Section: Introductionmentioning

confidence: 66%

“…A Variable Hard Sphere (VHS) model with velocity-dependent effective diameter is employed for neutral-neutral collisions calibrated to lithium vapor's temperature-dependent viscosity. The form for the viscosity is given by [5] 10 #$ = 130.6 + 0.1014 • ( − 1000) − 4.55 • 10 #2 • ( − 1000) 3 Where T is in K and μ in SI units. This form is then fit to a T ω dependence over the range of 700 K -1000 K and ω is provided as an input parameter to SPARTA.…”

Section: Spartamentioning

confidence: 99%

“…Simulations of the Fusion Nuclear Science Facility (FNSF) design [6] with lithium-induced detachment in UEDGE [2] indicate that lithium recombines roughly where it is ionized, as shown in Fig 2. This implies that lithium ionized on a given field line contributes to the lithium density in the plasma, but in steady-state a roughly equal amount of lithium is recombined on the same field line. Following the approach developed in [3], this is simulated in SPARTA by assuming that all neutral lithium that crosses the plasma boundary is ionized there, and an equal amount is locally recombined. Upon recombination, the neutral lithium is given both a temperature and a directed energy along =⃑ of 0.2 eV.…”

Section: Plasma Modelmentioning

confidence: 99%

“…In earlier work [3] we examined the addition of baffles in SPARTA simulations of FNSF and modified the boundary conditions to be more realistic. The absorbing walls were changed to 300 -400 C lithium-coated surfaces with relatively little evaporation and zero reflection.…”

Section: Simulation Of the Fnsf Divertor Without Bafflesmentioning

confidence: 99%

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A simplified lithium vapor box divertor

et al. 2019

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A detached divertor plasma is predicted to be necessary to mitigate the heat fluxes and ion energy, and so sputtering, at the divertor plate of a fusion power plant. It has proven difficult in current experiments, however, to prevent the detachment front, once formed, from running up to the main plasma resulting in deterioration of pedestal performance. The lithium vapor box divertor is designed to localize a dense cloud of lithium vapor away from the main plasma, in order to induce detachment at a stable, distant location. The vapor localization is created by local evaporation and nearby condensation, a configuration inaccessible to non-condensing seed impurities. The UEDGE code has been used to show that stable detachment can be achieved in the Fusion Nuclear Science Facility with lithium vapor alone, giving a widely dispersed heat flux of ~ 2 MW/m 2 to the divertor walls. However, the model for lithium vapor transport in UEDGE is purely diffusive, determined by collisions of Li atoms with fixed plasma ions. The paper provides simulations of lithium vapor flow using the SPARTA Direct Simulation Monte Carlo (DSMC) code, in which the lithium vapor dynamics are governed by Li-Li collisions that should dominate in regions with little plasma. The plasma model implemented in SPARTA is based on the UEDGE results for the location of ionization and recombination. We find that a simplified lithium vapor box configuration, without baffles, provides robust stabilization of the detachment front and acceptable lithium vapor flow to the main chamber. Lithium is evaporated from a capillary porous surface on the private-flux side of the divertor, distant from the main plasma, and is condensed on the other side walls of the divertor chamber. The condensed lithium flows back to the evaporator through 2 cm internal diameter pipes. The capillary pressure differential at the surface of the evaporator is capable of overcoming MHD back-force in the piping, with a great deal of margin if a sandwich flow channel insert is implemented. Very little lithium should be accumulated on the first wall of the main chamber if it is maintained at 600 C, as expected for a power-producing fusion system.

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Section: Introductionmentioning

confidence: 66%

Section: Spartamentioning

confidence: 99%

Section: Plasma Modelmentioning

confidence: 99%

Section: Simulation Of the Fnsf Divertor Without Bafflesmentioning

confidence: 99%

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A simplified lithium vapor box divertor

et al. 2019

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“…The lithium vapor box is a divertor design that seeks to control the detachment front by taking advantage of differential pumping [7]. By evaporating lithium close to the divertor target and placing condensing surfaces between the target and the X-point, a vapor density gradient can be created [8,9]. As the detachment front moves towards the X-point, less lithium will be at the ionization front, causing less energy loss, thus preventing further movement of the detachment front towards the X-point.…”

Section: Introductionmentioning

confidence: 99%

Predictive Modeling of a Lithium Vapor Box Divertor in NSTX-U using SOLPS-ITER

Emdee

Goldston

Lore

et al. 2021

Preprint

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The unmitigated heat flux in attached operation of a fusion power plant is predicted to be destructive to any solid divertor surface. Detachment, whereby the plasma pressure drops significantly before reaching the divertor target thus greatly reducing the heat flux and sputtering, will be necessary to ensure adequate lifetime of plasma facing components (PFCs). The lithium vapor box divertor aims to detach the divertor plasma via evaporating and condensing lithium surfaces. By evaporating lithium near or at the divertor plate and condensing it closer to the main chamber, a lithium vapor density gradient can be created. This density gradient ties energy losses to poloidal distance between the target and the detachment point. The radiation zone is then prevented from reaching the X-point as the lithium ionization rate decreases when the detachment front moves away from the divertor target. Here we present Scrape Off Layer Plasma Simulator (SOLPS) simulations of a lithium vapor box divertor using an NSTX-U equilibrium and PFC geometry. The parameters for the core boundary conditions, gas puff intensity, and heat and particle transport coefficients are chosen to match experimental values. Acceptable agreement with experimental Scrape-Off Layer (SOL) widths is found, indicating a reasonable choice of transport coefficients. In predictive simulations, lithium is added via evaporation at the target. Predictions for peak heat fluxes and upstream impurity concentration are given for a variety of evaporation rates. Target electron temperature is predicted to be able to be reduced to recombination levels (below 1 eV) for lithium evaporation rates of 1 • 10 23 Li/s, indicating detachment. Peak heat flux at the lower outer target could be reduced by as much as a factor of six while maintaining upstream lithium fractions below 2%. The prevention of lithium from reaching the midplane is shown to be due to an increase in frictional forces acting on the lithium from a deuterium gas puff. Lithium is also shown to be redeposited close to the evaporator which is favorable for initial tests and future capillary porous systems.

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