Liquid lithium (Li) divertor concepts offer a promising solution for managing the extreme heat fluxes expected in future fusion reactors. However, lithium’s strong affinity for hydrogen isotopes raises concerns regarding tritium inventory requirements and tritium breeding ratio. In particular, the lack of studies on tritium-lithium co-deposits is critical, as such co-deposits may contribute significantly to tritium retention in inaccessible areas, complicating tritium recovery. High-temperature retention measurements in co-deposits and in-situ outgassing studies from fully saturated LiD samples are scarce. In this work, we investigate Li-D co-deposits formed under high-flux deuterium plasmas (flux: ∼ 7 m−2s−1) in the linear plasma device Magnum-PSI to form several µm thick co-deposits. selective laser melting-based tungsten capillary porous structures filled with Li were exposed to D plasmas, while stainless steel witness plates placed nearby were used to collect the deposits. The Li:D ratio was analyzed across a temperature range of 160C–520C, followed by one-hour vacuum outgassing (0.04 Pa) at 200C–500C. Additional experiments studied the influence of D puffing (20 Pa D2) during outgassing and the role of residual gases in freshly deposited films. in-situ ion beam analysis was employed to characterize the co-deposits: nuclear reaction analysis quantified the Li and D areal densities, while elastic backscattering spectroscopy measured oxygen content. Results show that the D:Li ratio in the co-deposits remains at 40:60 close to the theoretical maximum of 50:50 and is largely independent of substrate temperature up to 450C. However, residual water vapor present in the vacuum vessel was found to chemically react with LiD, forming Li2O and releasing D. This surface-mediated process primarily affects thinner films, leading to substantial D loss and explaining variations in D:Li ratio across samples from the same plasma exposure but with different thicknesses. At 520C, the 100 nm and 120 nm thick co-deposits were fully converted to Li2O before ion beam analysis, preventing conclusive retention measurements at this temperature. Notably, Li2O formation was found to increase D desorption at low temperatures but inhibit it at higher temperatures, modifying the expected outgassing behavior based on thermal release alone. These findings highlight that, to avoid significant tritium retention in Li-T co-deposits, tokamak surfaces may need to be maintained above 450C. Furthermore, water vapor plays a more influential role in retention and release processes than previously believed.
液体リチウム(Li)ダイバータ概念は、将来の核融合炉で予想される極端な熱流束を管理するための有望な解決策を提供する。しかしながら、リチウムの水素同位体に対する強い親和性は、トリチウムインベントリ要件とトリチウム増殖比に関する懸念を引き起こす。特に、トリチウム-リチウム共堆積物に関する研究の不足は重大である。そのような共堆積物は、到達困難な領域におけるトリチウム保持に大きく寄与し、トリチウム回収を複雑にする可能性があるからである。共堆積物における高温保持測定と、完全に飽和したLiD試料からのその場脱ガス研究は乏しい。本研究では、線形プラズマ装置Magnum-PSIにおいて、高フラックス重水素プラズマ（フラックス： ∼ 7 m−2s−1）下で形成されたLi-D共堆積物を調査し、数µm厚の共堆積物を形成した。選択的レーザー溶融法に基づくタングステン毛細管多孔質構造にLiを充填したものをDプラズ