Effects of irradiation and mechanical stress on the superconducting properties of candidate magnet conductors

Abstract

The effects of .radiation damage on the superconducting critical properties of candidate magnet materials are reviewed. Neutron, and charged-particle irradiation results• are covered. The discussion is restricted to effects in NbTi and the Al5-compound superconductors. The utility of these conductors in radiation fields is first explored by defining the magnitude of critical-property changes with the fluence of various irradiating particles. The physical mechanisms that couple the irradiation defects to the observed critical-property changes are discussed. Annealing/recovery data on irradiated materials are included where• they pertain to the understanding of the physical mechanisms involved, and thereQy to the desirability of magnet annealing in actual operating circumstances. Although among the Al5 compounds Nb 3 Sn is now the leading candidate for high-field magnet applications, results for other Al5 compounds that appear to be fabricable as conductors will also be covered. The general conclusions to be drawn for AlS's and NbTi operating in a fusion-magnet configuration are that total fluences on the order of a few x10 18 n/cm 2 over the life of the magnet offers no serious. problem to the magnet's properties. Annealing NbTi to room temperature is beneficial, annealing the Al5's is detrimental. The fluence limits are for the entire magnet, spots of higher fluence resulting from lesser shielding being not tolerable. The effects of both tensile and bending stresses on the properties of Nb 3 Sn filamentary conductors are also surveyed. Some new data on the synergism • *Work performed under the auspices of the U.S. Department of Energy.-2between irradiation and stress effects are also presented. The results are discussed in terms of materials limits in application, and also in terms of possible ways new fabrication techniques may extend the range of strain that is both tolerable and beneficial. I.