Chemical Characterization and Sputtered Ion and Deuterium Retention Measurements of Lithium and Boron Coatings Exposed to Low-Energy Deuterium and Helium Ions

Lithium has been shown to increase energy confinement and allow for stable plasma discharges in tokamaks, which makes it a candidate material for Plasma-Facing Components (PFCs). Boron injections are planned for NSTX-U and have been shown to lower impurity levels and reduce the H-mode power threshold leading to better plasma performance. Simulations on simultaneously lithiated and boronized surfaces show that chemical interactions between lithium and boron affect deuterium retention and the plasma-material interactions [1]. Our experiments used a Sample Exposure Probe (SEP), an ultrahigh vacuum suitcase enabling sample transfers between a Sample Exposure Station (SES) and surface analysis chambers where the surface can be further modified using ion irradiations and analyzed using surface analysis techniques [2]. Both boron and lithium vapor deposition sources were constructed and attached to the SES to produce high-purity lithium and boron coatings on candidate PFC samples attached to the SEP. Lithium and boron coatings were exposed to low-energy deuterium and helium ions. Sputtered species were directly measured using a mass spectrometer, and Temperature Programmed Desorption (TPD) was used to measure deuterium retention. X-ray Photoelectron Spectroscopy (XPS) and TPD were performed before and after ion exposure to determine chemical composition changes of the coatings. [1] F. J. Domínguez-Gutiérrez, et al., J. App. Phys. 123, 195901 (2018). [2] A. Maan, et al., Rev. Sci. Instrum. 91, 026104 (2020).