Erosion, formation of deposited layers and fuel retention for beryllium under the influence of plasma impurities

The impact of argon as a seeded plasma impurity on the plasma–material interaction properties of beryllium was studied in the PISCES-B linear plasma device. When exposed to pure deuterium plasma, the surface of beryllium forms a fine-scale grass-like structure and contains a significant fraction of deuterium, leading to the reduction of the sputtering yield. An argon fraction in plasma of 10% prevents the formation of rough surface and reduces the deuterium retention in the beryllium target by >50%. Consequently, the beryllium sputtering yield in the presence of argon remains at a level close to the prediction by the binary collision code TRIM. The total retention of deuterium in co-deposited layers remains at a similar level when argon is added, since a higher amount of deposited Be is compensated by a lower D/Be value. Aluminium also forms a fine-scale surface structure and displays a reduction of the effective sputtering yield when exposed to pure deuterium plasma and can therefore be considered as a non-toxic proxy for studying selected plasma–material interaction properties of beryllium. (paper)