Speaker
Description
Understanding tritium (T) and deuterium (D) retention in boron-coated tungsten (B/W) plasma-facing components is essential for next-generation fusion devices such as SPARC, ITER, and future commercial reactors, because wall retention sets the in-vessel T inventory and influences D/T recycling and wall pumping, with direct implications for safe operation and sustained plasma performance. In this work, we present the first time-resolved measurements of D uptake and release in PVD (physical vapor deposition) boron thin films deposited on polycrystalline W during low-energy ($<100$ eV) D plasma exposures at fluxes up to $\sim10^{22}$ m$^{-2}$s$^{-1}$ in the DIONISOS linear plasma device, representative of tokamak first-wall conditions. Measurements were performed in operando using 3 MeV $^3$He Nuclear Reaction Analysis (NRA) during plasma exposures.
The D retention in the B/W sample exhibited a four-phase temporal evolution: during plasma exposure, the D inventory initially increased with a steep slope, then decreased, then increased again, and finally decreased once more after the plasma was shut off. This behavior is attributed to physical and chemical erosion of the B layer, diffusion of D into the W substrate, and subsequent outgassing after the end of the plasma exposure. These time-resolved measurements provide insight into D recycling by showing how boronized W surfaces can act as a source and sink for D during tokamak-relevant plasma operation. From these measurements, erosion rates, erosion yields, and D/B ratios were inferred.
Additional experiments vary the initial thickness of the B layer to study how the dynamics of D retention change as the time required to fully erode the layer varies. The sample temperature is also varied, as it affects the dissociation of B-D and B-D-B bonds, chemical erosion, and D diffusion. In addition, we compare PVD laboratory made B/W samples with B/W samples prepared in tokamaks using glow discharge boronization (GDB) to assess how deposition methods and film history influence D retention behavior.