Deuterium Retention and Diffusion in ETP-10 Graphite Exposed to RF Plasma at Room Temperature

Isotropic graphite of ETP-10 was exposed to a deuterium rf-plasma at room temperature and depth profiles of deuterium near the plasma-facing surface were observed by a nuclear reaction analysis. The depth profile consisted of two parts, which were a peak at the surface and a gradual slope downward to the depths. The surface density of deuterium estimated from the peak area was saturated with longer time and hardly decreased after the exposure. This was explained by that the incident deuterium atoms from the plasma were absorbed on deuterium-free sites and absorbed atoms were not desorbed. The deuterium concentration in the bulk increased nearly in proportion to the square root of time and gradually decreased after the plasma exposure. This was explained by a simple diffusion model and an apparent diffusion coefficient was found to be 2x10⁻¹⁸ m²s⁻¹ from the depth profile.