Surface chemistry analysis of lithiated porous tungsten under deuterium irradiation

High-Z materials such as tungsten-based alloys and alloy composites are attractive for use as PFCs because of their low sputtering yield, high melting point, and high thermal conductivity [1]. However, the use of these high-Z PFCs poses challenges during transient event operation such as dust generation, surface melting, cracking, and droplet ejection [2]. A solution to protect the plasma from high-Z emission is to coat them with a liquid low-Z metal (e.g. lithium) in the liquid state to continually replenish Li and therefore maintain a low-Z plasma interface while tolerating both high steady-state and transient heat fluxes in the high-duty cycle environment of a fusion reactor [3]. A lithium coating was deposited on three porous tungsten substrates. Sample 1 was irradiated while Li was solid, sample 2 while Li was liquid, and sample 3 after Li had resolidified. All samples were irradiated with D2+ with a fluence of 1016/cm2. In-vacuo X-ray Photoelectron Spectroscopy (XPS) and Thermal Desorption Spectroscopy (TDS) were performed on the samples following D2+ irradiation. The work described here identifies the impact of intrinsic impurities (H2O, O2, C) on the surface chemistry of lithium films under D+ exposure. Analysis of in-vacuo XPS data is correlated to emission channels of D2+ species from TDS and compared to previous Li-O- D2+ interaction studies done on porous and non-porous substrates such as TZM, carbon and tungsten.



Work supported by DOE Contract DE-SC0021119



[1] G. Sinclair et al. Sci. Rep., 7, (2017), 12273

[2] F. L. Tabarés, Plasma Phys. Controlled Fusion, 58, (2016), 014014

[3] Nygren, R. E., and F. L. Tabarés Nucl. Mater. Energy 9, (2016) 6–21