FLUENCE DEPENDENCE OF DEUTERIUM TRAPPING IN GRAPHITE

The trapping of approximately 1 keV D in graphite at 300 K has been studied by thermal desorption spectroscopy, as a function of fluence, for fluences up to approximately 4 X 10(24) D/m2. In pyrolytic (HPG99) and line grain (EK98) graphite, the amount of retained deuterium was found to increase with increasing D+ fluence over the entire range studied. In a pseudo-monocrystal sample, however, the amount of retained deuterium did not increase significantly beyond the saturation concentration of approximately 2 X 10(21) D/M2. The difference in retention properties is attributed to the crystal structure of the graphite. The more porous structure of pyrolytic and fine-grain graphites allows the migration of thermalized D atoms beyond the implantation zone, where they may be trapped, adding to the total hydrogen inventory.