Critical-current changes in neutron-irradiated Nb3Sn as a function of irradiation temperature and initial metallurgy

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Abstract
Fast‐neutron irradiations have been performed on Nb3Sn wires to determine the roles of irradiation temperature and the unirradiated value of the critical‐current density (Jc0) on the changes in Jc. Four experiments were performed: low‐ (6 K) and high‐ (350 K) temperature irradiation of high‐ (2×1010 A/cm2 at 5 T and 4.2 K) and moderate‐ (0.8×1010 A/cm2) Jc0 material. The large increases in Jc for the moderate‐Jc0 material were independent of irradiation temperature; the increases were smaller for the high‐Jc0 material, and a significant difference was found for the two irradiation temperatures. The difference is attributed to the greater pinning capability of defect cascades over defect clusters in the high‐Jc0 material. The smaller amount of Jc recovery after a 300 K anneal, when compared with NbTi, can also be understood in terms of the defects responsible for the flux pinning.