Critical current enhancement in Nb3Sn by low-temperature fast-neutron irradiation

An advanced type of Nb3Sn composite wire was irradiated at ∼6 K with fast neutrons. The short-section critical current jc was measured at 4.2 K (after annealing to 77 K) in transverse magnetic fields up to 10 T. Before irradiation, jc at 4 T was 1.6×106 A/cm2. A fluence of 1.8×1018 n/cm2 increased jc for H≳2T, the enhancement increasing with field to 85% at H=10 T. After annealing to 540 K, roughly one-half the enhancement remained. These results are compared with those for an earlier similar material, but with a smaller jc before irradiation. For comparable fluences, the relative enhancement in the earlier material was unexpectedly less than in the improved samples.