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Erosion of Carbon in Dual-Beam Experiments: an Overview

Multi-species impact is of high relevance for fusion reactors, where, in addition to the hydrogen fuel, the He ash, impurity species (e.g., C and O), and in some cases injected elements are also present. Combined irradiation of graphite with relatively low-energy H+ (typically below 100 eV) and energetic (above 300 eV) hydrogenic and non-hydrogenic ions leads to an enhancement of the chemical erosion yield compared to the low-energy H+-only case. This is due to the additional energy deposition and associated lattice damage by the added energetic ions. Studies of combined species irradiation also have the potential to enhance our understanding of the mechanisms leading to erosion and hydrogen transport in graphite. Mixed isotope experiments with simultaneous H+–D+ irradiation of graphite led to the conclusion that thermalized H and D move and recombine on internal surfaces within the implantation zone. In contrast, during H+–D+ irradiation, methane molecules are formed at the end of range of the incident ions. Combined H+ and O+ irradiation of graphite leads to the formation of hydrocarbons, carbon oxides and water, with water being formed at the end of the O+ implant range.