Ejection of ionic species from lithium and lithium compounds by low energy hydrogen and noble gas ion irradiation

We have conducted experimental measurements that quantify ejected lithium and impurity species in the form of positive and negative ions from lithium compounds during irradiation by hydrogen or noble gas ions. Lithium is a candidate material for plasma-facing components (PFCs) of magnetic confinement fusion devices. Ionic states of ejected species can play an important role in the plasma-material interaction as those are strongly affected by the sheath potential. The experiments include ions incident at ultralow energies (< 100 eV), which is relevant to tokamak divertor environments. Experiments detected Li as a positive ion species and O and H impurities as negative ion species. Ne and Ar ion irradiations, which are commonly used for glow discharge cleaning, were found to be an efficient O and H removal method. D ion irradiation works more efficiently for O and H removal than H ion irradiation. Oxidation of Li enhanced the ejection of Li positive ions. We observed different concentrations of ejected species from the surface at different temperatures (300 K and 460 K). The kinetic energy was found to be different for each ejected species, which suggests different ejection mechanisms. Quantified ejection yields for each species and ion irradiation will be presented.