Graphite surface erosion and deformation

Bulk reactor-grade graphite and WCA graphite cloth were exposed to an atom and ion beam produced in a Hall accelerator. Samples exposed to hydrogen received a total dose of 1020 atoms/cm2 of 580-eV mean energy H0 and 5×1018 ions/cm2 of 875-eV mean energy H+. Samples exposed to helium received a total dose of 1020 atoms/cm2 of He0 and 5×1018 ions/cm2 of He+. During irradiation, the pressure in the sample region was governed by the partial pressure of the source gas (H2or He) and was at 47 mPa. The samples were then examined with a scanning electron microscope and an optical interference microscope to determine the surface damage. Upon exposure to H0 and H+, the bulk graphite and the graphite cloth samples showed substantial surface erosion. The amount of erosion was found to be strongly dependent on the sample surface temperature. Upon exposure to He+, blistering was observed on the graphite cloth sample. No measurable surface erosion of the samples exposed to He was observed with the scanning electron microscope.