Ternary Nb 3 Sn superconductors with artificial pinning centers and high upper critical fields

In this letter we demonstrate the development of ternary Nb 3 Sn multifilamentary conductors with artificial pinning centers (APC) which achieve high critical fields. These recently-developed conductors were tested in a 31 T magnet, and the results showed that their upper critical field ( B c 2 ) values at 4.2 K are 27–28 T, and irreversible field ( B irr ) values are above 26 T, values similar to or higher than those of best rod-restack-process (RRP) conductors. The non-Cu J c has been brought to nearly 1200 A mm −2 at 16 T and 4.2 K, comparable to RRP, in spite of the fact that the fine-grain Nb 3 Sn fractions in filaments are still low (20%–30%) and the grain sizes are still not fully refined (70–80 nm) due to conductor designs and heat treatments that are not yet optimized. The Nb 3 Sn layer J c at 4.2 K, 16 T is 4710 A mm −2 for the APC wire with 1%Zr, about 2.5 times higher than RRP conductors, in spite of the fact that its grain size is not yet fully refined due to insufficient oxygen and unoptimized heat treatment. An analysis is presented about the non-Cu J c that can be achieved by further optimizing the APC conductors and their heat treatments.