Post-irradiation thermal desorption spectroscopy of graphite and its relation to chemical sputtering

Thermal desorption behavior of various hydrocarbons from isotropic graphite irradiated by hydrogen ions is investigated. Such hydrocarbons as methane (CH4) and ethane (C2H6) revealed relatively large desorption rate, showing good accordance with their thermochemical stability. On the other hand, an activation energy of desorption for the observed hydrocarbons was essentially the same regardless of their chemical forms. Moreover, it was found to decrease with increasing hydrogen fluence in the range between 1x1020 to 1x1022 ions m-2. These results seem to indicate the interaction of hydrogen atoms and C-H complexes to form CH3 or CH2 radicals as a possible rate-determining step common to all hydrocarbons. The obtained results are then discussed as related to chemical sputtering, and the possible impact they may have upon fusion applications is also discussed. (orig.)