Studies of lithium deposition and D retention on tungsten samples exposed to Li-seeded plasmas in PISCES-A

Tabarés, F.L.; Alegre, D.; Baldwin, M.J.; Nishijima, D.; Simmonds, M.; Doerner, R.; Alves, E.; Mateus, R.

doi:10.1088/1361-6587/aa5bae

Cited by 5 publications

(5 citation statements)

References 20 publications

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“…About this issue, it should be pointed out that previous experiments with cold (T surface ≈ 100 °C) W samples exposed to Li-seeded H 2 glow discharge (GD) plasmas [14] found a lower hydrogen retention compared to pre-lithiated W samples later exposed to H 2 GD plasmas, suggesting that no extra hydrogenic retention will be produced by the lithium implantation in comparison to the expected on lithium simply deposited. Additionally, very promising results have been obtained in terms of fuel retention and Li film formation for hot W samples exposed to Li-seeded deuterium linear plasmas in the PISCES-A divertor simulator [50]. These results presented in the worst case a retention (atomic ratio) at T surface = 400 °C higher by two orders of magnitude compared with the retention found for our sample wlid10 prepared at the same surface temperature.…”

Section: Considerations For the Fuel Retention Associated To The W Fi...supporting

confidence: 61%

Temperature dependence of liquid lithium film formation and deuterium retention on hot W samples studied by LID-QMS. Implications for future fusion reactors

et al. 2018

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Liquid metal (LM) divertor concepts explore an alternative solution to the challenging power/particle exhaust issues in future magnetic fusion reactors. Among them, lithium (Li) is the most promising material. Its use has shown important advantages in terms of improved H-mode plasma confinement and heat handling capabilities. In such scenario, a possible combination of tungsten (W) on the first wall and liquid Li on the divertor could be an acceptable solution, but several issues related to material compatibility remain open. In particular, the co-deposition of Li and hydrogen isotopes on W components could increase the associated tritium retention and represent a safety risk, especially if these co-deposits can uncontrollably grow in remote/plasma shadowed zones of the first wall. In this work, the retention of Li and deuterium (D) on tungsten at different surface temperature (200 °C–400 °C) has been studied by exposing W samples to Li evaporation under several D2 gaseous environments. Deuterium retention in the W–Li films has been quantified by using laser induced desorption-mass spectrometry (LID-QMS). Additional techniques as thermal desorption spectroscopy, secondary ion mass spectrometry, profilemetry and flame atomic emission spectroscopy were implemented to corroborate the retention results and for the qualitative and quantitative characterization of the films. The results showed a negligible (below LID sensibility) D uptake at Tsurface = 225 °C, when the W–Li layer is exposed to simultaneous Li evaporation and D2 gas exposition (0.67 Pa). Pre-lithiated samples were also exposed to higher D2 pressures (133.3 Pa) at different temperatures (200 °C–400 °C). A non-linear drastic reduction in the D retention with increasing temperatures was found on the W–Li films, presenting a D/Li atomic ratio at 400 °C lower than 0.1 at.% on a thin film of ≈100 nm thick. These results bode well (in terms of tritium inventory) for the potential utilization of this material combination in a real reactor scenario.

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Section: Considerations For the Fuel Retention Associated To The W Fi...supporting

confidence: 61%

Temperature dependence of liquid lithium film formation and deuterium retention on hot W samples studied by LID-QMS. Implications for future fusion reactors

et al. 2018

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“…In addition, for most cases, the 50:50 D:Li ratio is within the error bar. We conclude that D retention levels in LiD co-deposits do not show ether thickness or temperature dependence up to 380 • C, in contrast to other studies [15,16]. The disagreement in results can be explained by the fact that in [15] retention studies were carried out in an D 2 gas atmosphere while the studies in this paper used D plasma.…”

Section: Discussion and Future Workcontrasting

confidence: 80%

“…The disagreement in results can be explained by the fact that in [15] retention studies were carried out in an D 2 gas atmosphere while the studies in this paper used D plasma. In [16] the lithium films were thinner than in our case with all but one case, at 130 • C, having Li content below the NRA detection limit. Moreover, the studies were not done in-situ leading to possible D desorption by chemical reaction with air.…”

Section: Discussion and Future Workcontrasting

confidence: 66%

“…There is little literature regarding Li-D co-depositions in a D plasma environment and with in-situ diagnostics. Tabares et al [16] exposed tungsten plates to lithium-seeded deuterium plasma at temperatures between 130 • C-600 • C. The measured Li and D content were below the NRA detection limit, for all but one case, at 130 • C. In this case the D/Li ratio was less than 10 −4 , which is similar to retention rates of D in W at this temperature [17]. Krat et al [18] conducted magnetron sputtering with D 2 onto a Li target, capturing both D and Li on a molybdenum substrate.…”

Section: Introductionmentioning

confidence: 99%

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Deuterium retention in co-deposition with lithium in Magnum-PSI: experimental analysis and comparison with SOLPS-ITER

Morbey,

Gonzalez,

Arnoldbik

et al. 2024

Nucl. Fusion

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The vapor-box is a liquid metal based design to cope with the demanding conditions of the divertor. This design relies on the recirculation of lithium by evaporation and condensation. An issue to this approach is the safety risks of Li-D/T formation and co-deposition on both the vapor-box walls - leading to possible recirculation impedance- and on the first wall leading to unacceptable tritium retention. Additively manufactured tungsten Capillary Porous Structure (CPS) samples filled with Li were exposed to high heat flux D plasmas in the linear plasma device Magnum-PSI and Li-D co-deposition was measured as a function of substrate temperature, estimated to be in the range 200-428 ${^\circ}$C and distance between 25-85 mm to the plasma beam center. The D:Li ratio was determined via in-situ ion beam diagnostics (NRA and EBS) and the spectra analyzed simultaneously to maximise the precision of the measurement. The experimental results approach close to the theoretical maximum at 40:60 D:Li ratio and the thickness of the deposited films was 0.02 - 3.2 $\mu$m. For witness plate temperatures above 400 ${^\circ}$C Li films under 150 nm in thickness were deposited and show lower D:Li ratios, as low as 5:95 D:Li ratio. At these temperatures the evaporation rate from the WPs is close to the deposition rate, and the decomposition pressure for LiD becomes comparable to the operational pressure in the vessel during the discharge. SOLPS-ITER simulations were also conducted to complement the experimental data. The results were used to narrow the range of CPS surface temperature to between $650-700$^{\circ}$C and determined that the D$^{+}$ plasma is largely replaced by Li$^{+}$ plasma close to the target surface. Further, the redeposition ratio of the lithium on the CPS surface is determined to be around 80$\%$, which matches well with the value determined from a quartz crystal microbalance. Due to limitations in the modeling of neutral interactions with Li coated surfaces, the SOLPS-ITER modeling does not well recreate the observed Li and D deposition layers on the WPs, indicating that this aspect of the modeling in Eirene needs improvement to accurately model plasmas containing significant quantities of Li. However, SOLPS-ITER simulations should be extended to include LiD molecules and improve the accuracy of heat flux towards the target to improve the comparison with experimental data.

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“…Lithium (Li), which is the most widely researched LM for this application, shows a high uptake of hydrogen isotopes (HI) by formation of lithium hydride due to its chemical affinity with hydrogen isotopes [8,9]. Only at higher temperatures where Li evaporation is high is retention expected to be low [10], although limited experimental evidence exists that under simultaneous deposition of Li and deuterium (D) retention could be lower [11]. Compared with Li, Sn offers a wide operational window due to its very low vapor pressure.…”

Section: Introductionmentioning

confidence: 99%

Deuterium retention in Sn-filled samples exposed to fusion-relevant flux plasmas

Vernimmen

et al. 2020

Nucl. Fusion

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Tin (Sn) is an attractive option for a liquid metal wall material for future fusion reactors. Control of tritium inventory is key for the successful operation of these reactors, but little data exists up until now on hydrogen isotope retention in Sn. Free surface Sn targets and Sn-based capillary porous structure targets were exposed to deuterium (D) plasma in nano-PSI and magnum-PSI respectively. The retained D inventory was determined using the methods of thermal desorption spectroscopy and nuclear reaction analysis. The retention dependence is somewhat complex due to the mixed composition of the exposed samples as well as their liquid nature. The D retained in both types of Sn targets was found to increase with increasing D plasma fluence. For free surface liquid Sn targets, both thermal desorption spectroscopy and nuclear reaction analysis measurements showed a negative relationship between D retention and sample temperature. For capillary porous structure Sn targets, D retained in the top layer measured by nuclear reaction analysis decreased with temperature while the total D retained measured by thermal desorption spectroscopy remained approximately constant. By extracting pure Sn pieces from the targets it was found that the amount of D retained in pure Sn was much lower than that in the whole Sn-based targets and was estimated to be about 10 −7 -10 −4 D/Sn. D retained at the Sn-wall interface was found to dominate the total amount of D retained in the whole sample and observed cavities between deposited Sn droplets and the wall are the leading candidates responsible for this. Cavity formation is proposed to be the main retention mechanism for D in liquid Sn targets, although enhanced solubility leading to supersaturation under a D plasma environment is mainly responsible for the observed higher D retention in pure Sn compared with normal solubility under D gas. When compared with tungsten, D in Sn samples is of the same order of magnitude at temperatures below 300 °C, but at higher temperatures at least one to two orders of magnitude higher, most likely due to D trapped in cavities.

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Studies of lithium deposition and D retention on tungsten samples exposed to Li-seeded plasmas in PISCES-A

Cited by 5 publications

References 20 publications

Temperature dependence of liquid lithium film formation and deuterium retention on hot W samples studied by LID-QMS. Implications for future fusion reactors

Temperature dependence of liquid lithium film formation and deuterium retention on hot W samples studied by LID-QMS. Implications for future fusion reactors

Deuterium retention in co-deposition with lithium in Magnum-PSI: experimental analysis and comparison with SOLPS-ITER

Deuterium retention in Sn-filled samples exposed to fusion-relevant flux plasmas

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