Re-deposition of lithium and boron coatings under high-flux plasma bombardment at normal and grazing magnetic incidence

Abrams, T.; Jaworski, M. A.; Kaita, R.; Nichols, J.H.; Temmerman, G. De; Berg, M.A. van den; Meiden, H.J. van der; Morgan, T.W.

doi:10.1109/plasma.2014.7012276

Cited by 11 publications

(21 citation statements)

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“…Equation (3) predicts that the erosion rate of LiD effectively plateaus at a value of about 0.1 above ~450 °C whereas the evaporation rate of pure Li will increase indefinitely. The low erosion rate of LiD, coupled with the extremely high re-deposition efficiency of eroded Li atoms (>99%) that has been observed in experiments [32] and simulations [34] imply very long lifetimes for a LiD coatings even at high PFC temperatures. It was estimated in [7] that the temperature limit for a liquid Li walls in a tokamak is <400 °C from a perspective of core impurity accumulation, but this study neglected the effects of the Li/D mixed-material, which were shown in this present work to become significant at D fluences approaching the areal density of the Li coating.…”

Section: Discussionmentioning

confidence: 84%

“…To summarize, the analysis method used is similar to the S/XB technique that has been previously used to diagnose Li erosion [30], but with several refinements. First, a cosine distribution for the eroding impurity species was incorporated, which is generally observed for planar evaporation [31] and sputtering at normal ion incidence [32]. Second, a compensation factor was added for eroding neutrals that do not ionize before escaping from the plasma column.…”

Section: Discussionmentioning

confidence: 99%

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Suppressed gross erosion of high-temperature lithium via rapid deuterium implantation

et al. 2015

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Lithium-coated high-Z substrates are planned for use in the NSTX-U divertor and are a candidate plasma facing component (PFC) for reactors, but it remains necessary to characterize the gross Li erosion rate under high plasma fluxes (>1023 m−2 s−1), typical for the divertor region. In this work, a realistic model for the compositional evolution of a Li/D layer is developed that incorporates first principles molecular dynamics (MD) simulations of D diffusion in liquid Li. Predictions of Li erosion from a mixed Li/D material are also developed that include formation of lithium deuteride (LiD). The erosion rate of Li from LiD is predicted to be significantly lower than from pure Li. This prediction is tested in the Magnum-PSI linear plasma device at ion fluxes of 1023–1024 m−2 s−1 and Li surface temperatures ⩽800 °C. Li/LiD coatings ranging in thickness from 0.2 to 500 μm are studied. The dynamic D/Li concentrations are inferred via diffusion simulations. The pure Li erosion rate remains greater than Langmuir Law evaporation, as expected. For mixed-material Li/LiD surfaces, the erosion rates are reduced, in good agreement with modelling in almost all cases. These results imply that the temperature limit for a Li-coated PFC may be significantly higher than previously imagined.

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Section: Discussionmentioning

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Suppressed gross erosion of high-temperature lithium via rapid deuterium implantation

et al. 2015

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“…momentum exchange with the incoming plasma flux. In [19] it is suggested that the total redepostion fraction R in fu-10 −4 10 −3 10 −2 10 −1 10 0 10 1 10 2 10 3 10 4 10 1 Figure 1: The maximum tolerable power density has been determined for a LL divertor target (blue) with thermal properties equal to the ITER-like monoblocks (red). This target has a lithium supply rate Γ supply of 10 25 m −2 s −1 , and a 0.1 mm top layer.…”

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confidence: 99%

Power handling limit of liquid lithium divertor targets

et al. 2018

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A model is formulated to make a first estimate of the maximum tolerable power of liquid lithium divertor targets, and to gain insight into their behavior in terms of lithium loss rate and surface temperature. The model, formulated as a simple analytical expression, states that the incoming power is balanced by heat conduction through the target and by the lithium which is dissipating energy in the plasma by ionizing and radiating. A target is considered to fail when the net lithium loss flux from the surface exceeds the available supply. The model is evaluated over a range of input parameters: lithium supply rate, surface layer thickness, redeposition coefficient, and dissipated energy per Li particle lost to the plasma. Based on the results, first, surface temperature locking is expected above a deposited power of ∼ 10 MW/m 2. Second, lithium targets are expected to be extremely robust against power deposited during short transient events. A surface layer thickness of 50 micron is sufficient to withstand 60 MJ/m 2 vertical displacement events or 20 MJ/m 2 disruptions.

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“…first, the gross erosion rate is found to be reduced below experiments conducted in low-flux devices and second, a high redeposition rate was calculated indicating strong trapping at the surface [26].…”

Section: The Temperature Limit Of Liquid Lithium Pfcsmentioning

confidence: 81%

“…While the diffusive process is temperature dependent, lithium penetration into the graphite substrate was observed to occur rapidly, on the order of minutes, even at room temperature [30]. Experiments comparing lithium coating lifetimes on graphite vs. a molybdenum alloy (TZM) substrate found a factor of 100 change in the available lithium at the surface of the substrate [26]. This indicates that the metallic substrate will serve as a more substantial source of lithium for plasma experiments than would be expected from graphitic surfaces.…”

Section: High-z Divertor Target Upgradementioning

confidence: 99%

Upgrades toward high-heat flux, liquid lithium plasma-facing components in the NSTX-U

Jaworski

Brooks

Kaita

et al. 2016

Fusion Engineering and Design

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Liquid metal plasma-facing components (PFCs) provide numerous potential advantages over solid-material components. One critique of the approach is the relatively less developed technologies associated with deploying these components in a fusion plasma-experiment. Exploration of the temperature limits of liquid lithium PFCs in a tokamak divertor and the corresponding consequences on core operation are a high priority informing the possibilities for future liquid lithium PFCs. An all-metal NSTX-U is envisioned to make direct comparison between all high-Z wall operation and liquid lithium PFCs in a single device. By executing the all-metal upgrades incrementally, scientific productivity will be maintained while enabling physics and engineering-science studies to further develop the solid-and liquid-metal components. Six major elements of a flowing liquid-metal divertor system are described and a three-step program for implementing this system is laid out. The upgrade steps involve the first high-Z divertor target upgrade in NSTX-U, pre-filled liquid metal targets and finally, an integrated, flowing liquid metal divertor target. Two example issues are described where the engineering and physics experiments are shown to be closely related in examining the prospects for future liquid metal PFCs.

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Re-deposition of lithium and boron coatings under high-flux plasma bombardment at normal and grazing magnetic incidence

Cited by 11 publications

References 1 publication

Suppressed gross erosion of high-temperature lithium via rapid deuterium implantation

Suppressed gross erosion of high-temperature lithium via rapid deuterium implantation

Power handling limit of liquid lithium divertor targets

Upgrades toward high-heat flux, liquid lithium plasma-facing components in the NSTX-U

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