Abstract
We report non-Cu critical current densities of 4 . 09 ⋅ 109 A/m2 at 12 T and 2.27 ⋅ 109 A/m2 at 15 T obtained from transport measurements on a Ti-alloyed RRP Nb3Sn wire after irradiation to a fast neutron fluence of 8.9 ⋅ 1021 m−2. These values are to our knowledge unprecedented in multifilamentary Nb3Sn, and they correspond to a Jc enhancement of approximately 60% relative to the unirradiated state. Our magnetometry data obtained on short wire samples irradiated to fast neutron fluences of up to 2.5 ⋅ 1022 m−2 indicate the possibility of an even better performance, whereas earlier irradiation studies on bronze-processed Nb3Sn wires with a Sn content further from stoichiometry attested a decline of the critical current density at such high fluences. We show that radiation induced point-pinning centers rather than an increase of the upper critical field are responsible for this Jc enhancement, and argue that these results call for further research on pinning landscape engineering.
Highlights
We report non-Cu critical current densities of 4 . 09 ⋅ 109 A/m2 at 12 T and 2.27 ⋅ 109 A/m2 at 15 T obtained from transport measurements on a Ti-alloyed restack rod processed (RRP) Nb3Sn wire after irradiation to a fast neutron fluence of 8.9 ⋅ 1021 m−2
Reducing the grain size further by lowering the heat treatment temperature would compromise the homogeneity of the A-15 layer, resulting in an adverse effect on Jc5
In an earlier publication we demonstrated that the critical current density of a multifilamentary Nb3Sn wire can be reliably evaluated from magnetometry data, if the sub-element geometry is known[13]
Summary
We report non-Cu critical current densities of 4 . 09 ⋅ 109 A/m2 at 12 T and 2.27 ⋅ 109 A/m2 at 15 T obtained from transport measurements on a Ti-alloyed RRP Nb3Sn wire after irradiation to a fast neutron fluence of 8.9 ⋅ 1021 m−2. Through extensive research efforts in the fields of materials science and superconductor technology they have come a long way from the early bronze-processed strands to state-of-the-art restack rod processed (RRP) and powder-in-tube (PIT) wires The former were limited to non-matrix critical current densities below 109 A/m2 at 4.2 K and 12 T, whereas the latter achieve 3 ⋅ 109 A/m2 at the same temperature and field, while having superior high-field properties due to upper critical field optimization by ternary element addition[1,2]. The two main strategies employed for improving the critical current density Jc were grain refinement and impurity doping The former strives to decrease the grain size by optimizing the heat treatment process, resulting in a higher density of grain boundaries, which have been known to be the dominant pinning sites in Nb3Sn for a long time[3]. These results suggest that the limits of Nb3Sn wires can be pushed further by engineering their pinning landscape, for instance by the introduction of nano-particles
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