Quantum Study of Hydrogen Interaction with Plasma-Facing Graphite and Boron Doped Graphite Surfaces

Hydrogen adsorption and absorption on carbon materials play an important role in plasma surface interactions in thermonuclear controlled fusion devices. The Density Functional Theory has been used in order to investigate the interaction of hydrogen atoms with the basal (0001) plane of pure graphite and boron-doped graphite; these materials are taken as models of carbon armor of plasma facing components in tokamaks. We have shown that hydrogen adsorbs weakly on the graphite surface making the adsorbent carbon tetrahedral (sp3). It can also penetrate into the bulk through the surface aromatic cycles with a barrier of energy low compared to the energy of the impinging particles coming from the boundary plasma of tokamaks. Boron doping reinforces strongly the CH bonding energy and decreases dramatically the energy barrier associated to hydrogen diffusion into the bulk. We have also investigated the H2 recombination on the same substrates through Eley-Rideal and Langmuir-Hinshelwood mechanisms