Helium concentration in tungsten nano-tendril surface morphology using Elastic Recoil Detection

Helium (He) concentrations in tungsten nano-tendrils (W fuzz) have been measured for the first time using Elastic Recoil Detection (ERD). Fuzzy and non-fuzzy W surfaces were analyzed in order to illuminate the role of He in the transition in surface morphologies. Samples grown in the PISCES-A and PILOT-PSI experiments allowed a survey of surface temperature ranging from Ts 470–2595 K and of He fluence on the order of ΦHe ∼1024–1027 ions/m2. He concentrations measured in the bulk of W fuzz layers are roughly uniform with bulk He concentration 1–4 at.% while samples with just He in the near surface peaked at 1–2 at.%. This confirms that the nano-tendrils are filled with high pressure He bubbles since the solubility of He in W is ∼10−5 at.%. This indicates that the ∼1000 K temperature fuzz-growth threshold is determined by the response of the W, not the near-surface He concentration.