We reply to the comment by Li et al (submitted to Nucl. Fusion with this response) on our recent paper Nishijima et al (2023 Nucl. Fusion63 126003). In this response, we address the existence of an incident ion energy, Ei, threshold for the deuterium (D) supersaturated surface layer (DSSL) formation with a newly conducted D plasma exposure experiment at Ei ∼ 20 eV. It is also further demonstrated, based on new experiments where the ion flux, fluence, and sample temperature are scanned, that non-kinetic (ballistic) processes play a role in the DSSL formation and growth. In addition, the effect of impurities in our plasma is discussed also with a new analysis of the surface composition made after a D plasma exposure.
This paper responds to a comment on their previous work, which found that the formation of a deuterium-supersaturated surface layer (DSSL) on tungsten depends on the energy of the incident ions. The authors present new experiments showing that a minimum ion energy is required for DSSL formation, and that non-kinetic processes also play a role. They also discuss the effect of impurities in the plasma on the surface composition.