Performance Boost in Industrial Multifilamentary Nb3Sn Wires due to Radiation Induced Pinning Centers

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.

Unified Scaling Law for flux pinning in practical superconductors: II. Parameter testing, scaling constants, and the Extrapolative Scaling Expression

“…This stability reflects the intrinsic nature of unified scaling when the basic pinning mechanism is unchanged over the range of fields, temperatures and strains under consideration. A similar persistence of scaling was obtained by Baumgartner et al (2014Baumgartner et al ( , 2015, even when a second pinning mechanism was introduced. that temperature extrapolations can be carried out with the Hybrid1 and Hybrid2 h(t) models from data above ∼4 K down to 2.26 K, with RMS extrapolation errors of only 0.3%-0.8%.…”

“…Similar changes in the shape of the master scaling curves were found for the OST-RRP ® conductor, shown in appendix figure A2. A shift in the pinning force curve was also found by Baumgartner et al (2014Baumgartner et al ( , 2015 when Nb 3 Sn samples were neutron irradiated. The shift was modeled in terms of a second point-pinning mechanism being introduced by radiation.…”

Ternary Nb3Sn superconductors with artificial pinning centers and high upper critical fields

“…2, along with the reference RRP wire. The data points are fitted with the commonly-used two-component pinning force model [11], which has been proven by several studies to work well for APC conductors [7,11,19]. As can be seen from Fig.…”

“…It is shown in [4] that there are three factors determining the non-Cu Jc of a uniform Nb3Sn conductor: fine-grain (FG) Nb3Sn fraction within subelements, irreversibility field (Birr), and fluxon pinning capacity; of the three, the greatest potential for further improving non-Cu Jc lies in enhancing fluxon pinning [4]. For example, proton or neutron irradiation on reacted Nb3Sn conductors [7,8] demonstrated significantly improved non-Cu Jcs by introducing point pinning centers (e.g., to the record-breaking 2270 A/mm 2 at 4.2 K and 15 T [7]), although using irradiation processing for wind-and-react Nb3Sn magnets is difficult. In fact, introducing additional pinning centers (APC) to Nb3Sn conductors has long been a "holy grail" in the Nb3Sn community, with various efforts on a number of techniques since the 1980s, but none succeeded in making high-Jc wires [9][10][11][12][13].…”

Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density Nb3Sn Superconductor Wires

“…We conclude that improvements of Jc properties in the >16 T range at 4.2 K are still possible, also perhaps by using longer and higher HT temperatures to make the layers more compositionally uniform (recognizing of course that more effective diffusion barriers must be provided to protect the outer stabilizing Cu too). Although high field Jc can also be enhanced by increasing the density and effectiveness of flux pinning sites by decreasing the grain size, adding pinning centers 25,26 or introducing point pinning by irradiation, 27,28 these techniques do not raise Hc2. Thus, consideration of these surprising site disorder results should also be incorporated into any enhanced pinning center approach in order to raise the high field Jc.…”