Basic study on lithium coating and plasma-surface processes

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1. Establishment of Lithium Coating TechniqueLithium coating with evaporation method is investigated. It was found that the evaporation speed can be easily controlled by the oven temperature around 400 C.To suppress impurity from heated oven, RF inductive heating is used, which effectively heat the lithium itself without heating other materials.2. Chemical reaction of lithium with various gasesChemical reactivity of lithium film with various gases such as O_2, H_2, CH_4 or CO was investigated. It is found that the lithium is highly reactive with the oxygen gas, and the coated lithium film is completely oxidized when the oxygen gas is fed into the vessel. CO and CH_4 are also reactive with lithium, but reaction is limited up to a few monolayrs of lithium film surface. Hydrogen does not react with lithium film.3. Interaction of lithium film with hydrogen plasmaInteraction of lithium film with hydrogen DC glow plasma is investigated. Lithium film absorbs large amount of hydrogen. Hydrogen absorption is almost comparable to the coated lithium, which implies that the one lithium atom reacts with one hydrogen atom, and that the hydrogen penetrates into bulk of lithium film irrespective to the ion implantation range of hydrogen ion into the lithium film (less than a few hundred nano-meters).4. Lithium coating of JIPPT-IIU fusion experiment device.Lithium coating is successfully applied to the JIPPT-IIU fusion experiment device at National Institute for Fusion Science. Lithium (0.5g) is evaporated on the vessel wall of JIPPT-IIU,with coating area of about Im^2. It was found that the hydrogen recycling is reduced in the initial stage of tokamak discharge, and that the oxygen and carbon impurities is reduced.