Melt ejection and melt motion of tungsten (W) as a plasma-facing material due to accidental thermal overload events are primary concerns for ITER and DEMO. Previous experiments have revealed that W-1 wt.% La2O3 is an effective material for suppressing cavitation under a single pulsed heat load (Yuan et al 2014 Nucl. Fusion54 083026). To further investigate this effect, both W and W-1 wt.% La2O3 (WL10) were subjected to multiple melt exposures in the high heat flux facility GLADIS and the tokamak ASDEX Upgrade (AUG). In GLADIS, H/He high-power neutral particle beams were used, with a total energy density of 41–50 MJ m−2 per pulse, adjusted by the pulse duration. In AUG, eight ELMing H-mode deuterium (D) plasma discharges (#37680–87) were employed with samples exposed by the divertor manipulator DIM-II. The results revealed that the surface and cross-sectional morphologies of the resolidified melt layers are similar in both GLADIS and AUG. The pure W samples exhibited pronounced cavitation, with numerous spherical voids in the resolidified layer. In contrast, the WL10 samples developed an undulating surface morphology with a dense resolidified layer at the top, free of spherical voids and lanthanum particles, indicating sustained cavitation suppression even after La2O3 had vaporized from the top surface during previous melting. This suppression effect is likely primarily due to the formation of the undulating surface, which exposes the still La2O3-rich deeper material regions. The La2O3 particles participated in subsequent melting cycles, continuously preventing cavitation. Additionally, we compared D retention in W and WL10 samples subjected to the eight D plasma discharges in AUG. D retention was significantly reduced from 2.5 × 1021 to 4.4 × 1019 D m−2 for W and slightly decreased from 1.5 × 1021 to 1.2 × 1021 D m−2 for WL10 when comparing unmolten and molten samples. Overall, multiple melting experiments in both GLADIS and AUG confirm that W-La2O3 is a good cavitation-resistant material, effectively suppressing cavitation in W melt.
This paper investigates the effects of adding lanthanum oxide (La2O3) to tungsten (W) to suppress cavitation (formation of voids) during repeated melting events. Experiments in GLADIS and ASDEX Upgrade showed that W-La2O3 samples had an undulating surface and a dense resolidified layer without voids, indicating sustained cavitation suppression even after La2O3 evaporated from the surface. This is likely due to the undulating surface exposing La2O3-rich deeper regions. The La2O3 particles also participated in subsequent melting cycles, continuously preventing cavitation.