First-principles molecular dynamics study of plasma-surface interactions

Experiments show that the hydrocarbon molecules CH3 and CH4 in fusion devices are generated mainly by chemical sputtering. We numerically examine the chemical sputtering of graphite by hydrogen atoms by using the first-principles molecular dynamics simulation method based on quantum mechanics. We have shown that hydrogen atoms adsorbed on graphite break the carbon bonding of the graphite and hydrocarbon molecules are formed when they cover about half of the graphite surface. This occurs because an unstable configuration with a non-flat surface is formed due to adsorption of large numbers of hydrogen atoms. Moreover, we have shown that graphite is destroyed more actively in the high temperature region that models the actual fusion environment.