observation of the degradation of irradiated materials used in the first Q.2 commercial fission reactors. The technological challenges of fusion energy are intimately linked with the availability of suitable materials capable of reliably withstanding the extremely severe operational conditions of fusion reactors. Although fission and fusion materials exhibit common features, fusion materials research is broader. The harder mono-energetic spectrum associated with the deuterium-tritium fusion neutrons (14.1 MeV compared to <2 MeV on average for fission neutrons) releases significant amounts of hydrogen and helium as transmutation products that might lead to a (at present undetermined) degradation of structural materials after a few years of operation. Overcoming the historical lack of a fusion-relevant neutron source for materials testing is an essential pending step in fusion roadmaps. Structural materials development, together with research on functional materials capable of sustaining unprecedented power densities during plasma operation in a fusion reactor, have been the subject of decades of worldwide research efforts underpinning the present maturity of the fusion materials research programme.S ince Isaac Newton unravelled gravitation in the 17th century, Today, the nuclear fusion of a deuteron ( 2 H) and a triton ( 3 H) 28 is considered to be the most promising reaction for a commercial 29 fusion power plant: 2 H + 3 H → 3 He (3.5 MeV) +n (14.1 MeV).

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