Abstract
Helium plasma irradiation on metal surfaces leads to the formation of metallic fuzzy nanostructures accompanied by the growth of helium bubbles in metals. The mechanism of the growth process, its impact for fusion devices, and potential application have been explored. Here we show enhanced growth of large-scale fuzz by precipitating additional metallic particles during helium plasma irradiation. The growth rate of the fuzzy structures became orders of magnitude greater than conventional fuzz growth; in an hour of irradiation, 1 mm-thick visible tungsten and molybdenum fuzzy fur structures covered a tungsten metal substrate. Additional precipitation of metallic ions breaks the bottleneck diffusion process; moreover, further acceleration in the growth rate could have occurred if the electric sheath shape was influenced by the grown structure and the electric field that formed around the structure started collecting ions.
Highlights
The interaction between tungsten (W) and helium (He) is an important issue in a fusion environment
This is different from conventional He plasma irradiation, in which the surface becomes totally black with the formation of the nanostructured layer; rather, the sample surface was covered with visually identifiable fur-like material with a thickness of 0.5–1 mm
The growth rate decreased with the irradiation time; a time on the order of 108 s, i.e., three years, was required to grow a 1 mm fuzzy layer when we extrapolated from the conventional growth model
Summary
The interaction between tungsten (W) and helium (He) is an important issue in a fusion environment. The growth of nanostructures called fuzz on metallic surfaces due to helium plasma irradiation was initially identified on W surfaces in a demonstration of a fusion environment[3,4,5,6]. The question of whether the fuzz will be formed on plasma facing materials remains unanswered This is because the necessary conditions shown in[7], regarding the temperature and the incident ion energy, may not be satisfied in so-called detached or partially detached regimes. We show enhanced growth of large-scale metallic nanostructures by He plasma irradiation with the help of an additional precipitation of metallic particles on the surface. Scale bar in (c–f) and (g–i) represents 2 and 0.1 mm, respectively
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