Hydrogen retention in lithium on metallic walls from “in vacuo” analysis in LTX and implications for high-Z plasma-facing components in NSTX-U

Kaita, R.; Lucia, M.; Allain, Jean Paul; Bedoya, F.; Bell, R. E.; Boyle, Dennis; Capece, Angela M.; Jaworski, M. A.; Koel, Bruce E.; Majeski, R.; Roszell, J.P.; Schmitt, J. C.; Scotti, F.; Skinner, C.H.; Soukhanovskii, V.

doi:10.1016/j.fusengdes.2016.06.056

Cited by 22 publications

(11 citation statements)

References 20 publications

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“…Shown in figure 3(a), the molecular and plasma oxidation of fresh lithium films yields O:Li = 0.39 ± 0.08, consistent with XPS measurements at the edge of LTX where O:Li ≈ 0.5 and suggesting the formation of Li 2 O [17]. The discrepancy is probably due to the pre-oxidation resulting from the migration of oxygen from the underlying material into the fresh lithium.…”

Section: Oxygen Gettering Properties Of B(c)/lisupporting

confidence: 71%

“…The discrepancy is probably due to the pre-oxidation resulting from the migration of oxygen from the underlying material into the fresh lithium. This pre-oxidation is unaccounted for by our method and happens on a timescale of several minutes [17]. For this reason, all trials are initiated within tens of seconds after the deposition.…”

Section: Oxygen Gettering Properties Of B(c)/limentioning

confidence: 99%

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Boron synergies in lithium film performance

Devitre

Oyarzábal²,

Fernández-Berceruelo³

et al. 2020

Nucl. Fusion

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Fusion experiments use lithium and boron getters to capture impurities and control the density of fuel species in the plasma. In the TJ-II Stellarator, the addition of a boron-carbon substrate was found to extend the lifetime of the very reactive lithium wall conditioning. However, the synergies between the lithium layer and the underlying boron-carbon, or the effect of a glow discharge cleaning, on oxygen and deuterium gettering are not fully understood. Laboratory experiments were therefore initiated to gain deeper insight on the getter properties of B(C)/Li walls. The coatings were exposed to oxygen gas and plasmas while the capture and release of O was followed by mass spectrometry. Without the boron substrate, the maximum oxygen uptake is half the number of lithium atoms in the film for both oxygen gas and oxygen plasma. Conversely, the behaviour of B(C)/Li walls depends on the nature of the oxidation process: molecular oxygen (O:Li ≈ 0.15) or plasma (O:Li ≈ 0.50). The oxygen plasma gettering is thus preserved against molecular oxidation, e.g. an overnight exposure to the residual gas. While oxygen is known to promote hydrogen retention in lithium, the oxygen content of a B(C)/Li coating shows little effect on deuterium retention. Unlike simple lithium, the oxygen and deuterium gettering of B(C)/Li recovers after a helium glow discharge treatment. These advantageous features clearly point to a change in chemistry, with complex interactions between film constituents and the oxygen-rich environment of magnetic fusion devices.

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Section: Oxygen Gettering Properties Of B(c)/lisupporting

confidence: 71%

Section: Oxygen Gettering Properties Of B(c)/limentioning

confidence: 99%

Boron synergies in lithium film performance

Devitre

Oyarzábal²,

Fernández-Berceruelo³

et al. 2020

Nucl. Fusion

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“…Later experiments with electron-beam evaporation showed additional improvements, including good performance using liquid lithium coatings [35,36]. Using the Materials Analysis and Particle Probe (MAPP) to make in vacuo measurements, it was determined that while the surface was mostly oxidized within a few hours, the solid lithium coatings were still effective at pumping hydrogen [37][38][39].…”

Section: Pacs Numbersmentioning

confidence: 99%

Observation of Flat Electron Temperature Profiles in the Lithium Tokamak Experiment

et al. 2017

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“…The authors reasoned the formation of LiH layer to be responsible for the observations as the LiH thermally decomposed at temperature more than 400 • C. Exposing the Li coated (3 monolayers Li film) Molybdenum substrates to flux of diatomic deuterium ions [12], it has been observed that the molecular D 2 has been released at temperatures ∼300 • C in highly oxidized Li film substrate due to loosely bound D 2 , while in pure metallic Li film substrate, the D 2 has been released at ∼430 • C due to LiD decomposition. The experiments in lithium tokamak experiments (LTX) also suggests the fresh Li coating and oxygen contained Li coating are capable for retaining hydrogen species in high Z as well as in graphite PFCs [13]. Deuterium retention/decomposition is also observed in liquid Li divertor (LLD) made up of porous molybdenum in NSTX [14].…”

Section: Introductionmentioning

confidence: 96%

Lithium wall conditioning techniques in ADITYA-U tokamak for impurity and fuel control

et al. 2021

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In fusion devices, various techniques are employed for coating the plasma facing components (PFCs) including the vessel wall with low-Z material like lithium, boron, and silicon in order to enhance the plasma parameters and control. In ADITYA-Upgrade tokamak, different techniques of lithium wall conditioning are developed and implemented to obtain uniform and sustainable coating of Li on PFCs and the vessel wall. In this paper, two techniques used to generate Li from the source are reported. In one of the technique, a heated (fixed temperature of ∼120 °C) Li-rod is placed inside the hydrogen glow discharge cleaning (H-GDC) plasma and the sputtered Li by hydrogen (H) ions and atoms coats the wall and periphery. In the second technique, the Li is vapourized using a high-temperature Li-evaporator and released into the H-GDC plasma for uniform coating of Li on the PFCs and vessel. Significantly enhanced plasma parameters are obtained after Li coating by both techniques, with the evaporated Li performed better than the Li rod case. With the Li coating obtained with evaporated Li at 600 °C (550 mg Li) with H-GDC, the Li wall conditioning has been observed to be sustaining for in a larger number of plasma discharges in comparison to non-H-GDC assisted Li deposition. As the melting temperature of lithium hydride (LiH) is much higher (688.7 °C) than that of lithium (180.5 °C), this enhance the longer Li-coating lifetime relatively due to the formation of Li–H molecules on the vessel wall and PFCs. In ADITYA-U the carbon impurity and hydrogen recycling, due to relatively high surface area of graphite PFCs as well as their proximity to the plasma, limits the plasma performance and effective controls. Hence, H-GDC, H-GDC with Li-rod sputtering or Li evaporation, helium-GDC, argon–hydrogen mixtures-GDC in particular sequence are carried out to obtain better plasma discharges. The Li coating techniques and their effect on tokamak plasma discharges of ADITYA-U are discussed in this paper.

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Hydrogen retention in lithium on metallic walls from “in vacuo” analysis in LTX and implications for high-Z plasma-facing components in NSTX-U

Cited by 22 publications

References 20 publications

Boron synergies in lithium film performance

Boron synergies in lithium film performance

Observation of Flat Electron Temperature Profiles in the Lithium Tokamak Experiment

Lithium wall conditioning techniques in ADITYA-U tokamak for impurity and fuel control

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