Artificial Pinning in Nb3Sn Wires

Two different processes are known to create “artificial” pinning centers in superconductors: 1) high energy irradiation; and 2) nanoinclusions. Own results on the critical current density Jcof Nb3Sn wires after irradiation by protons are compared to the effects obtained by neutrons (on the same wires) and by nanoinclusions from the literature. Characteristic differences and similarities are discussed. After high energy irradiation, the observed enhancement of Jcis attributed to the formation of defect clusters. The contributions due to grain boundary pinning on one hand and of point pinning on the other can be separated, using a two-component model. This is in contrast to wires with nanoinclusions, where point pinning effects occur simultaneously to those due to enhanced grain boundary pinning, as a consequence of a reduction of the A15 grain size. In both cases, the enhancement ΔJcin Nb3Sn wires decreases gradually with increasing applied field and vanishes at Bc2. In binary Nb3Sn wires with oxide nanoinclusions, an increase of Jcby 100 A/mm2with respect to the present RRP wires is expected at fields between 17 and 18 T.