Effect of Neutron Irradiation on the Critical Current of Nb₃Sn at High Magnetic Fields

The changes in the critical current Ic of multifilament Nb3Sn following several fission-reactor-neutron irradiations at ∼60°C have been investigated as a function of applied transverse magnetic field up to 160 kG. Increases in Ic below 1018 n/cm2 (E > 1 MeV) show a strong field dependence, relative changes being larger as the field increases. These increases are attributed to increases in Hc2 brought about by irradiation-induced increases in the normal-state resistivity of the superconductor. For doses >1018 n/cm2, sharp decreases in Ic are observed, but the behavior of Ic is qualitatively identical for all fields from 40 to 160 kG. Therefore, data obtained at the more easily attainable lower magnetic fields are directly applicable to the high-field regions in this high-fluence regime. However, for fluences below ∼1018 n/cm2, magnetic-field-dependent measurements are required to determine the response of the superconductor to the neutron irradiation.