Chemical and physical erosion of carbon and metallic substrates containing lithium during low-energy deuterium ion irradiation

Lithium deposition on Grade ATJ graphite substrates and metallic substrates under low-energy D2+ irradiation are compared. Transient and steady-state release rate of ejected species are measured for non-lithiated and lithiated ATJ graphite surfaces. Irradiation fluxes of order 10¹⁵ cm^-2 s^-1 exposed samples while ejected species are monitored with a line-of-sight quadrupole mass spectrometer. For lithiated ATJ graphite the dominant D emission channels are D₂O and HDO and indicate the importance of lithium, water breakdown at the surface and oxide formation on desorption dynamics. Exponential decay in the transient release rate of ejected species is found for lithiated ATJ graphite, indicating that near surface super-saturation of D atoms at the vacuum interface in the presence of lithium atoms. In situ X-ray photoelectron spectroscopy (XPS) surface analysis corroborates this result. Lithium-coatings on Mo substrates demonstrate high sputtering rates; however depleted Li/Mo surfaces are quickly recovered when surfaces are heated to temperatures near 500 K.