Three-dimensional morphology of blister-like structures and deuterium retention in tungsten exposed to low-energy, high-flux D plasma

Three dimensional morphology of blister-like structures and deuterium retention in recrystallized tungsten have been examined after exposure to a low-energy (38 eV/D), high-flux (1022 D/m2s) deuterium plasma at ion fluences in the range from 1026 to 1027 D/m2 and various temperatures. The methods used were scanning electron microscopy equipped with focused ion beam, thermal desorption spectroscopy, and the D(3He,p)4He nuclear reaction at 3He energies varied from 0.69 to 4.0 MeV. Blister-like structures with various shapes and sizes depending on the exposure fluence and temperature are formed on the W surface. In doing so, cracks with distorted areas (<600 K) and large cavities (100-1000 μm3) at grain boundaries (≥500 K) were observed beneath the surface. The surface blister-like structures and the defects underneath are correlated along crystallographic orientation of the W grains in accordance to the low-indexed sliding systems. The defects are mobile and accumulate under D plasma exposure. Samples exposed near room temperature do not form such large cavities even by subsequent heating up to 1300 K. The D plasma exposure at temperature above 700 K dose not lead to formation of blister-like structures. At ion fluences of 1026-1027 D/m2, the D retention increase with the exposure temperature, reaching its maximum value of about 1022 D/m2 at 480-530 K, and then decreases to about 1019 D/m2 at 800 K. (author)