Enhancement of j c at 10-12 T in Nb 3 Sn wires by artificial Ta inclusions distributed at a nanometre scale

The effect of uniaxial strain on the critical current of 0.8 m long Nb 3 Sn wires up to 21 T is studied by the modified Walters spring (WASP). For Nb 3 Sn wires, prepared by both the bronze route and the internal Sn diffusion process, the critical current density as a function of the uniaxial strain ε is found to exhibit an asymmetric behaviour on both sides of the strain ε m , where J c reaches its maximum. Revisiting earlier x-ray and neutron diffraction measurements on bronze route processed wires between 10 and 600 K, it is shown that the asymmetric behaviour of J c (ε) on both sides of the strain value ε m is connected to individual variations of the stress-induced tetragonal lattice parameters a and c.The present measurements of J c versus strain for Nb 3 Sn wires show stronger strain dependence for wires prepared by the internal Sn diffusion method with respect to those obtained by the bronze route. The reasons for this difference are attributed to the individual details of the filament configuration in both types of wire, for example the different Sn distributions inside the filaments and the very different filament sizes, 4 and 80 µm, respectively.

Section: Comparison Between the Behaviour Of J C (ε) For Both Wire Typesmentioning

confidence: 99%

Asymmetric behaviour ofJ_c(ε) in Nb₃Sn wires and correlation with the stress induced elastic tetragonal distortion

Flükiger

Uglietti

Abächerli

et al. 2005

“…A common theme has been to try to reduce the A15 grain size and to introduce additional pinning centres (APCs) into the Nb3Sn. Ta [20] and Cu [21,22] inclusions were tried without great benefit to Jc, although major effects on enhancing HMax were reported by Rodrigues [22]. The most effective recent results are those observed by irradiation.…”

Section: Introductionmentioning

confidence: 99%

Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb₃Sn with and without an O source

Balachandran

Tarantini

Lee

et al. 2019

Here we show that addition of Hf to Nb4Ta can significantly improve the high field performance of Nb3Sn, making it suitable for dipole magnets for a machine like the 100 TeV future circular collider (FCC). A big challenge of the FCC is that the desired non-Cu critical current density (Jc) target of 1500 A/mm 2 (16 T, 4.2 K) is substantially above the best present Nb3Sn conductors doped with Ti or Ta (~1300 A/mm 2 in the very best sample of the very best commercial wire). Recent success with internal oxidation of Nb-Zr precursor has shown significant improvement in the layer Jc of Nb3Sn wires, albeit with the complication of providing an internal oxygen diffusion pathway and avoiding degradation of the irreversibility field HIrr. We here extend the Nb1Zr oxidation approach by comparing Zr and Hf additions to the standard Nb4Ta alloy of maximum Hc2 and Hirr. Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and without SnO2 and their properties measured over the entire superconducting range at fields up to 31 T. We found that group IV alloying of Nb4Ta does raise HIrr, though adding O2 still degrades this slightly. As noted in earlier Nb1Zr work with an O source, the pinning force density Fp is strongly enhanced and its peak value shifted to higher field by internal oxidation. A surprising result of this work is that we found better properties in Nb4Ta1Hf without SnO2, FpMax achieving 2.35 Times that of the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54 times that of the Nb4Ta alloy. The highest layer Jc(16 T, 4.2 K) of 3700 A/mm 2 was found in the SnO2free wire made with Nb4Ta1Hf alloy. Using a standard A15 cross-section fraction of 60% for modern PIT and RRP wires, we estimated that a non-Cu Jc of 2200 A/mm 2 is obtainable in modern conductors, well above the 1500 A/mm 2 FCC specification. Moreover, since the best properties were obtained without SnO2, the Nb4Ta1Hf alloy appears to open a straightforward route to enhanced properties in Nb3Sn wires manufactured by virtually all the presently used commercial routes employed today.

“…The main application of Nb 3 Sn wires is the fabrication of high field superconducting solenoids and dipoles. The wires fabricated by the Bronze Route technique [1] are characterized by a large number (up to 15 000) of filaments whose diameter is of the order of 4 µm. The Sn content in the filaments varies between 17 and 25 at.% [1,2].…”

Section: Introductionmentioning

confidence: 99%

Specific heat of Nb₃Sn wires

Wang¹,

Senatore²,

Abächerli³

et al. 2006

Multifilamentary superconducting Nb 3 Sn wires are widely used for industrial applications. Wires processed by the Bronze Route technique are characterized by a large number of filaments Nb 1−x Sn x , with 0.18 x 0.25, corresponding to a distribution of T c between <10 and 18 K. This distribution is a critical property of the wires and is important for the optimization of the conductors. However, it is not accessible to conventional techniques, due to percolation and/or magnetic shielding effects. In order to determine the T c distribution in the sample, we have carried out specific heat measurements of various Nb 3 Sn multifilamentary wires (including the bronze matrix) in zero field and at 14 T. A deconvolution of the calorimetric data at the superconducting transition by means of a thermodynamical model was used for obtaining the distribution of T c in the whole wire volume. The measurements were extended to Nb 3 Sn wires containing Ti additions, and the results were compared. The present calorimetric method is of primary importance for the complete characterization of Nb 3 Sn wires.