Chemical erosion of pyrolytic graphite by low-energy H+ and D+ impact

Recent developments have lead to prospects of lower plasma edge temperatures in the divertor region of tokamaks and, consequently, a growing interest in the interaction of graphite with low-energy hydrogen ions (10s of eV). Here we present experimental measurements of methane and heavier hydrocarbon yields of pyrolytic graphite (300 K-1000 K temperature) for Hf impact energies of 10-200 eV. Heavier hydrocarbons contribute significantly to the total chemical erosion yield at low energies. Comparison of CH4 yields due to H+ irradiation of graphite with similar results for CD4 yields due to D+ shows a smaller isotopic effect than anticipated based on previous H+ and D+ measurements. Comparisons are also made between the experimental results and a recently proposed model.