Helium-W co-deposition layer: TEM observation and D retention

Co-deposition of wall material and ions from plasmas occurs on material surfaces in fusion devices. In this study, we focus on tungsten (W) deposition layer in helium (He) plasmas (He-W co-deposition) formed at surface temperatures of 473–773 K. Usually, He irradiation at the surface temperature below 1000 K does not lead to significant morphology changes; we will show from transmission electron microscope observations that the roughness of the co-deposition layer has a significant temperature dependence even when the temperature is less than 800 K. We conducted deuterium plasma irradiation to the He-W co-deposition layer. It was found that the deuterium retention on the He-W co-deposition layer increased significantly with increasing the formation temperature of the co-deposition layer.