Erosion and dust formation of graphite materials under low-energy and high-flux atomic hydrogen irradiation

Experiments on erosion and dust formation have been conducted in argon-hydrogen mixture plasma irradiation of isotropic graphite targets. In this experiment, the dominant erosion process of the graphite target is chemical sputtering by low-energy atomic hydrogen irradiation. The chemical sputtering yield by low-energy atomic hydrogen irradiation has been roughly estimated to be 0.001-0.005, which is in the same range as those obtained by energetic hydrogen ion irradiation. It is found that the chemical sputtering yield strongly depends on the atomic hydrogen flux in the present experiments as well as that in fusion experiments. Many dust particles with various shapes and structures are observed on the graphite targets in the erosion dominant condition. It is also found that the shape, size and number density of the dust particles are strongly related to the target surface temperature Ts. Increasing Ts up to 1100 K turns the spherical particles into polyhedral crystalline diamond.