DEEP PENETRATION OF DEUTERIUM IN CARBON BASED SUBSTRATES EXPOSED TO THE PISCES-A PLASMA

Carbon based substrates were exposed to the PISCES-A high flux deuterium plasma, i.e. pyrolytic graphite, a carbon fibre material, the same material coated with a layer of SiC, and a graphite composite containing 30% SiC. The sides of the samples facing the plasma were again analysed after 1½ years of storage. In both analyses, the same amount of retained deuterium was detected, except for the carbon fibre, for which a drop in the front surface concentration of about 35-40% was found. The bulk of the samples was investigated. To analyse the inner parts of the exposed materials, the samples were cleaved; before cleaving, they were covered on all sides by a layer of lacquer to avoid contamination of the new surfaces by deuterium (dust) from the outside of the samples. For carbon fibre, it was found that deuterium had penetrated several millimetres into the material; this is much deeper than what had been expected from previous analyses. In the pyrolytic graphite sample, deuterium penetrated to about 1 mm depth, but the profile was much steeper than that for carbon fibre. For carbon fibre covered by SiC (∼ 1 μm layer), no deuterium was found inside the sample, indicating that the SiC layer was impermeable for deuterium. Also the graphite composite sample contained no deuterium. © 1990 IOP Publishing Ltd.