Tungsten co-deposited layers in fusion devices are a significant potential source of plasma-contaminating dust. This study investigates the mechanisms of dust release from helium–tungsten (He–W) and deuterium–tungsten (D–W) layers under high-density steady-state plasma and ELM-like plasma pulse superposition. High-speed imaging revealed different emission behaviors: the D–W layer, featuring pre-existing blisters, released dust immediately upon plasma exposure, while the He–W layer showed a delayed emission requiring damage accumulation from several pulses. Post-mortem SEM analysis confirmed distinct surface exfoliation corresponding to these behaviors. The immediate release of D–W dust was identified as the rupture of inherently fragile blisters. In contrast, the delayed release of He–W dusts resulted from subsurface flaking, initiated by horizontal cracks forming from the interconnection of internal nano-cavities. Both layers produced substantial dust, leading to much higher erosion rates than that of pristine tungsten. These results demonstrate that the trapped gas species fundamentally dictates the co-deposited layer’s microstructure and subsequent dust emission pathway, establishing these layers as a critical and rapid dust source under transient plasma loads.
Dust in fusion devices - experimental evidence, possible sources and consequences