Jcchanges after neutron irradiation of Nb3Sn at 8 K

In order to understand radiation effects in fusion magnet materials under operating conditions, the critical current (Jc) and critical temperature (Tc) have been measured up to 3.2 T as a function of dose after fast neutron irradiation at 6 K in Nb3Sn¹and after thermal neutron irradiation at 8 K in 0.1 a/o²³⁵U-Nb3Sn. Experimentally determining an equivalent fast-neutron dose for the latter fission-fragment damage allows comparison of the irradiations. Increases in high Jcmaterial (1.5 × 10⁶A/cm²at 4.5 K and 3.2 T) where observed after 1 × 10¹⁸n/cm²(E > 0.1 MeV). An extension of the dose up to 2.5 × 10¹⁹n/cm²resulted in decreases in Jcby a factor of 20 and decreases in Tcfrom 18 to 11 K. The results are explained by a model that considers enhanced flux pinning (Fp) by the radiation-induced defect cascades at low doses. At higher doses the decreases in Tcdominate and lower Fp. The field dependence of the Fpchanges can be explained by considering changes in Hc2The model predicted the observed Jcchanges in the²³⁵U-Nb3Sn. The Jcchanges differ from those found after neutron irradiations at ∼400 K due to the different flux pinning characteristics of the different defect structures.