D retention in Be exposed to fusion relevant mixed species D${}_2-$He plasma

Highlights: • D retention in Be is explored in ITER relevant D₂ and mixed species D${}_2-\alpha$He plasma exposure with up to 10% (α = 0.1) He ions in the incident plasma flux. • With α = 0.1, A threefold reduction in D retention is found for target exposure temperature ∼300 K. • The reduction diminishes toward ∼473 K, and is not apparent above 473 K. • The reduction is associated with an ability of He to hinder the accumula- tion of D in low-release temperature, supersaturated binding states in the Be target surface. • The reduction mechanism is not understood, but the implications toward T inventory assessment/control are encouraging for reactors utilizing Be, particularly Iter. - Abstract: He admixture to D₂ plasma incident on Be targets is used to study the influence of a fusion-ash relevant He concentration on D retention. A variation of exposure parameters such as He ion fraction: 0.02 ≤ α ≤ 0.1, exposure temperature: 330 ≤ T_exp ≤ 650 K, ion-fluence: 5 × 10²⁴ ≤ Φ ≤ 1 × 10²⁷ m${}^{-2}$ and energy: 40 ≤ E_i ≤ 90 eV, are explored. Results are compared to D retention values in Be observed in D₂ plasma ($\alpha =0$). With $\alpha =0.1,$ a factor ∼3 reduction in D retention is noted for exposure at ∼300 K, but is less as T_exp approaches ∼473 K, and not apparent above 473 K. The reduction is caused by the ability of He to hinder D saturation in low-release-temperature supersaturated binding states.