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

概要

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A systematic study has been carried out on Nb-Ti wire of two different kinds of metal-lurgical structure, to examine the effects of neutron irradiation on the critical density Jc. The samples used were Nb-47.6 a/0 Ti (sample #A) and Nb-59.8 a/0 Ti (sample #B), which were aged at 380°C for 0104 min and irradiated to 1.3 × 1018n/cm2 (En>0.1 MeV). The sample temper-ature during the irradiation is believed to have been below 70°C. The values of Jc 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 Jc 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 Tc. The Tc of #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 Tc. 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 Jc upon irradiation. It is concluded that super-conducting Nb-Ti wire with Jc 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.