High temperature annealing of ion irradiated tungsten

Transmission electron microscopy of high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications (500-1200 °C). Bulk isochronal and isothermal annealing of ion irradiated pure tungsten (2 MeV W+ ions, 500 °C, 1014 W+/cm2) with temperatures of 800, 950, 1100 and 1400 °C, from 0.5 to 8 h, was followed by ex situ characterisation of defect size, number density, Burgers vector and nature. Loops with diameters larger than 2-3 nm were considered for detailed analysis, among which all loops had b=12〈111〉 and were predominantly of interstitial nature. In situ annealing experiments from 300 up to 1200 °C were also carried out, including dynamic temperature ramp-ups. These confirmed an acceleration of loop loss above 900 °C. At different temperatures within this range, dislocations exhibited behaviour such as initial isolated loop hopping followed by large-scale rearrangements into loop chains, coalescence and finally line-loop interactions and widespread absorption by free-surfaces at increasing temperatures. An activation energy for the annealing of dislocation length was derived, finding Ea=1.34±0.2 eV for the 700-1100 °C range.