Temperature impact on the micro structure of tungsten exposed to He irradiation in LHD

helium plasma in the LHD. Samples were exposed to estimated fluences of similar to 10(23) m(-2) and temperatures ranging from 65 to 600 degrees C. Transmission Electron Microscopy analysis allowed the study of the impact of He irradiation under high temperatures on tungsten micro structure for the first time in real-plasma exposure conditions. Both dislocation loops and bubbles appeared from low to medium temperatures and saw an impressive increase of size (factor 4 to 6) most probably by coalescence as the temperature reaches 600 degrees C, with 500 degrees C appearing as a threshold for bubble growth. Annealing of the samples up to 800 C highlighted the stability of the dislocation damages formed by helium irradiation at high surface temperature, as bubbles and dislocation loops seem to conserve their characteristics. Additional studies on cross-sections showed that bubbles were formed much deeper (70-100 nm) than the heavily damaged surface layer (10-20 nm), raising concern about the impact on the material mechanical properties conservation and potential additional trapping of hydrogen isotopes. (C) 2016 Elsevier B.V. All rights reserved.