Interaction of powerful hot plasma and fast ion streams with materials in dense plasma focus devices
We have examined conditions and parameters of irradiation of materials perspective for use in the mainstream nuclear fusion facilities for two devices of the Dense Plasma Focus (DPF) type (PF-6 and PF-1000) with a number of diagnostics in comparison with conditions expected in the first-wall materials in Iter and NIF. It is found that a so-called “damage factor” helps in modelling of the fusion reactor conditions. Optical microscopy, SEM, Atomic Emission Spectroscopy, images in secondary electrons and in characteristic X-ray luminescence of different elements, and X-ray elemental analysis, present results for a number of materials including low-activated ferritic and austenitic stainless steels, β-alloy of Ti, as well as the double-forged W (candidate material for divertor in Iter). With an increase of the power flux density of hot plasma and fast ion streams irradiating the surface, its morphology changes from a weak wave-like structure of the surface to the strongly developed one for the same material. It was melted with the appearance of the fracturing pattern – first along the borders of grains and then with the intergranular net of microcracks. At the highest values of power flux densities multiple blisters appeared. Besides, in this last case cracks develop because of microstresses at the solidification of melt. Presence of deuterium within the surface nanolayers of irradiated ferritic steel is explained by capture of deuterons in lattice defects of the types of impurity atoms, pores and oxycarbonitride particles presented in the material.