Applications of large superconducting magnets, e.g. in particle accelerators or in nuclear fusion devices, require a safe magnet operation over the plant lifetime. Therefore, "material test programmes" in a specific radiation environment to simulate the operating conditions of the magnet and to assess the radiation response of each of the magnet components are essential.
In a brief introduction, I’ll review the radiation environment expected at the magnet location of a fusion device, either of ITER or of design studies for later fusion power reactors. According to the present state of the art, the magnets will consist of metallic superconductors operating at liquid helium temperatures, i.e. stabilised multifilamentary conductors made from Nb3Sn or similar compounds, and of glass-fibre reinforced epoxies as the insulation material.
Experimental results on the radiation-induced changes of the critical current densities Jc, the transition temperature Tc and the upper critical field Hc2 of the superconductors, on the resistivity of the stabiliser, and on the mechanical and electrical properties of the insulating materials will be presented and evaluated in terms of the requirements set for this application. We will conclude that the currently envisaged superconductors are suitable for ITER, but that the insulation will need modifications, i.e. the epoxies will have to be replaced by radiation-harder compounds (cyanate ester / epoxy blends). The corresponding qualifica tion programmes for ITER are currently under way at ATI.
Finally, radiation effects on high temperature superconductors will be discussed. Although these materials are presently not suited for the construction of superconducting high field magnets operating in the liquid nitrogen temperature range, they will certainly play an important role in the future. The results show that irradiation of these materials by suitable particles, in particular fast neutrons, leads to an enormous improvement of their flux pinning capability. Considering the rapid developments in this field of research, in particular the dramatic improvements in the processing technologies, predictions on their role in future fusion devices are somewhat premature. It is, however, obvious that extended dedicated R&D efforts will be required to reach this goal.