Flashover lithium ion source development

The authors have found that water and hydrocarbon surface contaminants (adsorbates) contribute over one-half of the ion beam current extracted from an uncleaned lithium flashover source. They have developed methods to generate high purity (85%) lithium ion beams from these sources, either by vacuum baking combined with glow discharge cleaning, or by in-situ deposition of the ion source material. However, concurrent with this improvement, they have observed a significant decrease in the extracted ion current, from over 1.2KA/cm/sup 2/ from an epoxy source to less than 0.3KA/cm/sup 2/ from a cleaned lithium dielectric flashover source. The authors believe this high impedance diode behavior reflects the difficulty with which lithium is desorbed from an ionic lithium dielectric material compared to the easily desorbed adsorbates. This observation is supported by recent ESD and PSD studies which show that the vast majority of lithium is desorbed from LiF as ground state, neutral lithium via a slow thermal process (compared to the 40 ns diode power pulse). Several methods have been suggested to improve this situation