Hydrogen species in diamond: Molecular dynamics simulation in bulk diamond for fusion applications

For an electron cyclotron resonance heating system, a diamond window seems to be the only material able to withstand the high microwave power and radiation effects and at the same time act as a tritium barrier. Therefore it is important to understand the evolution of hydrogen isotopes in diamond. Both, hydrogen content and radiation can quite rapidly degrade its excellent properties. Hydrogen isotopes can be introduced in the material by two processes: (1) during the growth process of synthetic samples and (2) as a neutron radiation effect when devices are exposed to a fusion irradiation environment. In the last case, both device performance (thermal, optical and dielectric properties degradation) and hands-on maintenance of the window (tritium inventory), demand a good knowledge of hydrogen species concentrations and their evolution with lattice damage.In this paper, a classical molecular dynamics study analyses the hydrogen equilibrium sites in diamond, and also their bulk and interstitial vibrational characteristics, including isotopic shifts. Some interesting results are presented and discussed. We confirm that the bond-centred site is the more stable configuration for H. Vibrational studies show lines in the C–H stretching region. Isotopic studies reveal ratios close to the theoretical ones for BC and ET sites. On the contrary, the AB site vibrations obtained suggest the existence of a local carbon oscillation.