Neutron irradiation effect on critical current of Nb3Sn wire under 8 T to 15.5 T

Abstract

Superconducting magnets for fusion application will be irradiated by fast neutrons produced by fusion reaction, and it has been reported that the superconducting properties of the superconducting wires vary drastically by the irradiation. A bronze route Nb₃Sn wire and an internal tin process wire were irradiated in a fission reactor up to 1.7 × 10²³ n/m² (> 0.1 MeV neutron), and the change in the critical current was measured by 15.5 T superconducting magnet and a variable temperature insert. The 4.9 × 10²² n/m² irradiation for the bronze route wire increased the critical current by 1.75 times, but the 7.9 × 10²² n/m² irradiation showed 1.03 times increase for the bronze route wire and 0.72 times decrease for the internal tin process wire. The 1.7 x 10²³ n/m² irradiation for the internal tin process wire decreased the critical current severely and the critical magnetic field down to around 16 T. This was the first result that the high fluence neutron irradiation caused the degradation of both the critical current and the critical magnetic field in this type of a Nb₃Sn wire. Some irradiation defects will become the magnetic flux pining sites and strengthen the pining force. But the strong irradiation will damage the superconducting phase and degrade the properties.