Isotope dependence of the chemical erosion of graphite by hydrogen/deuterium implantation

Abstract

Since graphite material is still a candidate for parts of planned fusion devices as ITER, the chemical erosion by hydrogen isotopes is a major concern. At energies of the impinging hydrogen below 100 eV, a strong isotope effect of the chemical erosion of carbon at low temperature is observed by hydrogen and deuterium ion impact. This effect is diminished at elevated temperatures around 800 K. For energies of the impinging hydrogen ion around 200 eV, only a minor isotope effect is observed in the maximum erosion yield at temperatures around 750 K. At low temperatures, the chemical erosion yields for these ion energies are much smaller than those for ions below 100 eV. Hydrogen/deuterium ions with energies of 1 keV and above show no isotope effect at all. Also in fusion devices as JET, TEXTOR and JT-60 an isotope effect in the chemical erosion of carbon materials is observed. The erosion yield in deuterium plasmas (Te=10–50 eV) is 1.3–1.5 ofthat in a hydrogen plasma. The multi-step process of chemical erosion of carbon materials by hydrogen isotopes is reasonably understood. The isotope effect is mainly caused by the radiation damage of the incident ions and by the ion-induced release process. © 2002 Taylor and Francis Group, LTD.