Quantitative evaluation of resistance of plasma facing materials to helium plasma irradiation

The damage to Plasma-Faced Materials (PFMs) under helium (He) plasma irradiation includes upward fuzz growth and inward He bubble erosion. While current research on PFMs mainly focuses on fuzz growth, the equally critical issue of inward erosion into materials by high-flux, low-energy He plasma irradiation is often ignored. To fill this gap, we propose He bubble erosion thickness ( L ) as a quantitative metric to characterize the degree of He bubble erosion in PFMs induced by He plasma, defined as the thickness difference between the pristine sample and the remaining undamaged region after irradiation. Experimental studies on tantalum (Ta) and tungsten (W) films reveal that L follows a square-root dependence on He fluence, closely linked to He diffusion and He bubble formation. Similar to the diffusion coefficient of fuzz ( D ), the diffusion coefficient of He bubble erosion ( D' ) is introduced as a new quantitative parameter for evaluating the He bubble erosion rate of PFMs. A parameter, η, is further introduced to distinguish the dominant damage mode. Notably, designed Ta/W multilayer exhibits significantly reduced D and similar D′ values compared to W, which is attributed to semi-coherent interfaces and the formation of a Ta–W alloy within the fuzz. This study provides not only valuable parameters for PFM evaluation but also a promising strategy for designing future PFMs.