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

The changes in the critical current I_c 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 I_c 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 H_c2 brought about by irradiation-induced increases in the normal-state resistivity of the superconductor. For doses >10¹⁸ n/cm², sharp decreases in I_c are observed, but the behavior of I_c 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.