One of the known lithium conditioning effects was the reduction of carbon impurities released from the graphite walls of a tokamak. However, little was known about the role of lithium in graphite-plasma interactions. Graphite intercalates lithium atoms between the hexagonal layer planes. The Li diffusion constant in the direction perpendicular to the basal planes of highly oriented pyrolytic graphite was measured for the first time using Rutherford back-scattering spectrometry and was found to be D⊥ = 2.1 x 10-10cm2/s with an activation energy of 0.26eV, in the case of low temperatures (300K) and low Li concentration (Li/C atomic ratio <3%). This value increased by a factor of two when highly oriented pyrolytic graphite was exposed to hydrogen plasma before lithium deposition. The implications resulting from the Li-graphite intercalation in lithium wall conditioning were discussed, focusing on Li-induced suppression of graphite sputtering.

Rapid Diffusion of Lithium into Bulk Graphite in Lithium Conditioning. Itou, N., Toyoda, H., Morita, K., Sugai, H.: Journal of Nuclear Materials, 2001, 290-293, 281-5