Experimental reproduction of damages induced by W dust projectile impinging on W targets up to 3 km/s

Plasma facing components (PFCs) erosion in tokamaks is a well-known problem for a successful integrated tokamak reactor and for future fusion power plants for energy production [1, 2]. In fact the eroded material could migrate inside the plasma core, leading to an increase of Zef f of the plasma itself, and/or in other critical locations inside the vacuum vessel and on sensitive apparatus (such as microwave mirrors, optical windows, probe heads, antennas) rising problems during tokamak operations [3]. Moreover, eroded material can increase the dust inventory in the vacuum vessel leading to safety related problems [4]. The morphological analysis of craters found on FTU limiter tiles [5] has revealed a novel source of material erosion. In particular, energetic runway electrons (REs) strike the vessel wall and limiters causing an explosion-like event that leads to the ejection of fast, about 1km/s, solid dust. This heavy fast dust moves inertially and impinges on nearby PFCs leading to craters generation, cracks formation and the vaporization of co-deposited material. The experimental reproduction of damages, induced by W dust projectile impinging on W targets in the km/s speed range, could be useful to study possible damage in the last generation tokamaks, such as ITER, where REs could be an issue. In this report are present morphology analyses of craters resulting from shooting different sizes of W dust on W targets up to 3 km/s. The results of this investigation could then be used for the empirical formulation of a damage scaling law.