Challenges and Perspectives of the Phase Formation of Internally Oxidized PIT-Type Nb3Sn Conductors

Promising results of internally oxidized conductors based on Bruker's Powder-In-Tube (PIT) design are presented. SnO ₂ was used as an oxygen source and Nb1Zr/Nb2.5Ti were chosen as the Nb alloy precursor. At a reduced field of B/B _c2 = 0.5, an increase of more than 70% in non-Cu Jc against a standard PIT reference was measured. No correlation between oxygen content of the conductor core and grain size was observed. The performance increase was attributed to nanoscale precipitates that act as APC's and lead to an increased point pinning component in the internally oxidized samples. The lack of grain refinement is seen as the result of the formation of Nb-Sn intermetallics prior to the oxygen release and Nb3Sn formation that inhibit an adequate oxygen supply to the Nb alloy.