The trapping of 1keV D at 300K, when using fluences of up to 4 x 1024/m2, was studied by using thermal desorption spectroscopic techniques. It was found that, in the case of pyrolytic (HPG99) and fine-grained (EK48) material, the amount of retained D increased with increasing D+ fluence. However, in pseudo-monocrystalline material, the amount of retained D did not increase significantly beyond a saturation concentration of about 2 x 1021/m2. The difference in retention was attributed to the crystal structure of the graphite. The more porous structure of pyrolytic and fine-grained materials was suggested to permit the migration of thermalized D atoms beyond the implantation zone, where they could be trapped and add to the total H burden.

A.A.Haasz, J.W.Davis: Journal of Nuclear Materials, 1994, 209[2], 155-60