論文の公開元へThermal treatment of W large-scale fiberform nanostructures
概要
Tungsten (W) is a leading candidate material for plasma facing components in fusion devices because of its low sputtering yield and low tritium inventory. However, it has been recognized that the thermal and physical properties are significantly altered by the exposure to helium (He) plasmas, especially when fiberform nanostructures called fuzz are grown on the surface [1–5]. Concerning the fuzz growth, an acceleration in the growth rate has been recently identified with additional W deposition, and mm-thick large scale fiberform nanostructures (LFNs) are grown on the surface when a certain set of conditions is satisfied [6]. The acceleration in the growth rate has been identified in a magnetron sputtering device [7] in addition to linear plasma devices (NAGDIS-II [6] and Magnum-PSI [8]).
To answer the question whether fuzz is grown in fusion relevant conditions, it is important to discuss the counter- growth effects such as sputtering [9–11] and annealing [12–15] in addition to growth process [16]. Concerning the conventional fuzz growth, De Temmerman et al have considered those effects and showed that ∼1-µm-thick fuzz can be grown under fusion relevant condition, and that the energy of edge localized modes (ELMs) [17] is a key parameter for the fuzz growth [18]. However, thermal response of thick fuzzy layer formed with deposition including LFNs has yet to be fully understood. In this study, we perform thermal treatment and investigate morphology changes, annealing rate, and He desorption behavior of thick W fuzzy layer including LFNs formed under deposition conditions.
