A molecular dynamics study of diamond and graphite under tritium bombardment

Carbon has proven to be a promising plasma facing material in tokamak reactors because of its high thermal conductivity and limited radiative cooling as a plasma contaminant. It is used in a range of forms, mostly graphitic or amorphous. Diamond, however, has superior thermal properties to other forms of carbon but has been largely overlooked due to fears of graphitisation. Tritium retention is, perhaps, the major disadvantage of using carbon as a plasma facing material in a deuterium-tritium fusion reactor. Here, we use molecular dynamics to study the relative performance of diamond and graphite on exposure to tritium bombardment. We model the cumulative bombarded of diamond and graphitic surfaces with a high flux (10(29) m(-2) s(-1)) of low energy 15 eV tritium atoms. This was done for substrate temperatures in the range 300-2100 K. Below temperatures of graphitisation (similar to 1000 K) the diamond structure confined tritium to the upper surface, this inhibited further structural damage and resulted in lower total retention. The graphitic surface allowed for deeper tritium penetration and therefore greater retention. These results corroborate with recent experimental evidence. (C) 2011 American Institute of Physics. [doi:10.1063/1.3656988]