Neutron irradiation effects on A15 multifilamentary wires

Whereas Nb₃Sn wires are commercially available and produced in long lengths for the fabrication of large high field magnets, Nb₃Al is emerging as a candidate material for even higher fields, particularly for nuclear fusion devices. We are therefore investigating the basic superconducting parameters of both materials, such as the transition temperature, the critical current densities and the upper critical fields, as a function of gamma dose and fast neutron fluence. Whereas the transition temperature of these multifilamentary wires is found to decrease slightly, both J_C and the upper critical fields (as determined from Kramer plots) increase with neutron fluence, in agreement with previous work on A15 systems. The enhancement of the critical currents amounts to approximately 15%. Further irradiation work to higher fluences is under way, in order to investigate the limits of these materials for applications in a radiation environment.