The implications of mixed-material plasma-facing surfaces in ITER

In all plasma-confinement devices, material eroded from plasma-facing surfaces will be transported and redeposited at other, sometimes remote, locations. If the plasma-facing material in a device consists of more than a single element there is a high probability that the composition of the plasma-facing surfaces will evolve over time and may exhibit plasma-interaction properties much different from the originally installed material. These plasma-created materials, or mixed materials, are the subjects of this review paper which focuses on the ITER relevant mix of materials, namely carbon, tungsten and beryllium. Knowledge concerning the formation conditions, erosion behavior and hydrogen isotope retention properties of each binary combination of materials is described. Where available information concerning tertiary combinations of materials is discussed.