Neutron Irradiation Effects on Superconducting Nb-Ti Wires for Fusion Reactor

A systematic study has been carried out on Nb-Ti wire of two different kinds of metallurgical structure, to examine the effects of neutron irradiation on the critical density J c . The samples used were Nb-47.6 a/0 Ti (sample #A) and Nb-59.8a/0 Ti (sample #B), which were aged at 380°C for 0~10 4 min and irradiated to 1.3×10 18 n/cm 2 (E n 0.1 MeV). The sample temperature during the irradiation is believed to have been below 70°C. The values of J c of both #A and #B aged up to 50 min were found to increase with irradiation. But when aged beyond 100 min, #B had its value of J c lowered by the irradiation. The presence of Ti enriched precipitates such as α and ω phases in the samples was surmised from the behavior shown by the critical temperature T c . The T c of f #A and #B changed little by irradiation when aged not longer than 100 min, but with aging beyond 500 min, #B showed a decrease in its value of T c . This decrease indicates that the Ti concentration in the matrix may have increased through radiation-induced breakup of the above-mentioned precipitates, which, in turn, would have brought about the reduction observed in J c upon irradiation. It is concluded that superconducting Nb-Ti wire with J c endanced by precipitation does not appear very resistant to neutron irradiation. This underlines the importance of the choice of superconducting materials to be used in fusion reactor magnets.