Dynamic deuterium (D) retention properties of tungsten (W) are investigated under steady-state D plasma exposure in the PISCES-A linear plasma device. In contrast to static retention, dynamic retention is quickly released from the material at the termination of the incident plasma flux, and thus in-operando laser-induced breakdown spectroscopy (LIBS) measurements have been conducted during steady-state D plasma exposure. A procedure is, first, established to extract the dynamic retention component from the in-operando LIBS D I 656.1 nm line intensity, which can contain contributions from dynamic and static retention as well as background D/D2 gas, excited by both steady-state and laser-induced plasmas. Using the developed procedure, the dynamic D retention in W is systematically examined while scanning the following plasma exposure parameters: incident ion energy, Ei, sample temperature, Ts, incident ion flux, Γi. No clear Ei dependence is seen in the range of Ei ∼ 45–175 eV, as expected from a small variation in the average implantation depth (∼3–6 nm) of D in W. The dynamic retention is found to monotonously decrease with increasing Ts from 348 to 573 K, while the total static retention is reported to peak at Ts ∼ 500–600 K. It is revealed that the dynamic retention linearly increases with increasing Γi, and then saturates at Γi ⩾ 0.75 × 1021 m−2 s−1. Possible physical mechanisms for the observed dependence of the dynamic retention on Ts and Γi are discussed. Furthermore, sequential pure He, followed by pure D, plasma exposures show that the dynamic D retention is not strongly affected by He bubbles in the near-surface region.
Hydrogenic retention of high-Z refractory metals exposed to ITER divertor-relevant plasma conditions