Dynamic deuterium retention properties of tungsten measured using laser-induced breakdown spectroscopy

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/D-2 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, E (i), sample temperature, T (s), incident ion flux, Gamma(i). No clear E (i) dependence is seen in the range of E (i) similar to 45-175 eV, as expected from a small variation in the average implantation depth (similar to 3-6 nm) of D in W. The dynamic retention is found to monotonously decrease with increasing T (s) from 348 to 573 K, while the total static retention is reported to peak at T (s) similar to 500-600 K. It is revealed that the dynamic retention linearly increases with increasing Gamma(i), and then saturates at Gamma(i) > 0.75 x 10(21) m(-2) s(-1). Possible physical mechanisms for the observed dependence of the dynamic retention on T (s) and Gamma(i) 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.