Influence of heat treatment temperature and Ti doping on low-field flux jumping and stability in (Nb-Ta)<sub>3</sub>Sn strands

Xu, Xingchen; Sumption, M.D.; Collings, E. W.

doi:10.1088/0953-2048/27/9/095009

Cited by 17 publications

(30 citation statements)

References 42 publications

(51 reference statements)

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“…Further improvements are being pursued. respectively, which are about half of those RRP and PIT wires reacted at 650-675 °C [4,30], but much larger than the average grain sizes of the early APC samples with 1% Zr and sufficient O reacted below 650 °C, which were 35-45 nm [15,19,20]. For APC-A, this is because it was reacted at 675 °C and it had only 0.6%Zr in the Nb alloy: lower Zr content leads to fewer ZrO2 particles for grain refinement.…”

Section: Resultsmentioning

confidence: 99%

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

Rochester

Peng

et al. 2019

Supercond. Sci. Technol.

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In this letter we demonstrate the development of ternary Nb3Sn 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 (Bc2) values at 4.2 K are 27-28 T, and irreversible field (Birr) values are above 26 T, values similar to or higher than those of best RRP conductors. The non-Cu Jc 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 Nb3Sn 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 Nb3Sn layer Jc 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 Jc that can be achieved by further optimizing the APC conductors and their heat treatments.

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Section: Resultsmentioning

confidence: 99%

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

Rochester

Peng

et al. 2019

Supercond. Sci. Technol.

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“…Doping to Nb3Sn can be controlled via the additions to the precursors (e.g., Nb-7.5wt.%Ta, Nb-47wt.%Ti, or Sn-Ti), which is mature for present conductors. On the other hand, high Sn content typically requires high heat treatment temperature (e.g., Figure 5) which is undesirable as grain size increases exponentially with reaction temperature [55]. Evidently a fundamental understanding of what controls Nb3Sn stoichiometry is critical.…”

Section: A Theory For Nb3sn Stoichiometrymentioning

confidence: 99%

“…Heat treatment temperature can simultaneously influence multiple factors, such as chemical potential of Sn in the Sn source, diffusion rate of Sn in Nb3Sn, and reaction rates at Another factor that may influence the Sn content of Nb3Sn, according to the above theory, is the competition between the Sn diffusion rate across the Nb3Sn layer and the Nb-Sn reaction rate at the Nb3Sn/Nb interface. This effect has hardly been noticed; however, the phenomenon that Ti addition tends to accelerate Nb3Sn layer growth rate [55] and make the stoichiometry more uniform in the Nb3Sn layer [73] could be explained by this effect. It has been seen that Ti addition segregates at Nb3Sn grain boundaries and causes greater lattice distortion at grain boundaries, which is believed to cause higher grain boundary diffusivity [84].…”

Section: A Theory For Nb3sn Stoichiometrymentioning

confidence: 99%

A review and prospects for Nb₃Sn superconductor development

2017

Supercond. Sci. Technol.

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Nb3Sn superconductors have significant applications in constructing high-field (> 10 T) magnets. This article briefly reviews development of Nb3Sn superconductor and proposes prospects for further improvement. It is shown that significant improvement of critical current density (Jc) is needed for future accelerator magnets. After a brief review of the development of Nb3Sn superconductors, the factors controlling Jc are summarized and correlated with their microstructure and chemistry. The non-matrix Jc of Nb3Sn conductors is mainly determined by three factors: the fraction of current-carrying Nb3Sn phase in the non-matrix area, the upper critical field Bc2, and the flux-line pinning capacity. Then prospects to improve the three factors are discussed respectively. An analytic model was developed to show how the ratios of precursors determine the phase fractions after heat treatment, based on which it is predicted that the limit of current-carrying Nb3Sn fraction in subelements is ~65%. Then, since Bc2 is largely determined by the Nb3Sn stoichiometry, a thermodynamic/kinetic theory was presented to show what essentially determines the Sn content of Nb3Sn conductors. This theory explains the influences of Sn sources and Ti addition on stoichiometry and growth rate of Nb3Sn layers. Next, to improve flux pinning, previous efforts in this community to introduce additional pinning centers (APC) to Nb3Sn wires are reviewed, and an internal oxidation technique is described.Finally, prospects for further improvement of non-matrix Jc of Nb3Sn conductors are discussed, 2 and it is seen that the only opportunity for further significantly improving Jc lies in improving the flux pinning.

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“…For Nb 3 Sn, improvement in critical current density can be realized by refining grain size . Present day Nb 3 Sn strands have average grain sizes of typically 100–200 nm .…”

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Internally Oxidized Nb₃Sn Strands with Fine Grain Size and High Critical Current Density

Sumption

Peng

2015

Advanced Materials

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Nb 3 Sn superconducting strands are the most practical conductors to generate high magnetic fields (12-16 T), and thus have significant applications in nuclear magnetic resonance (NMR), and great potential for fusion reactors and particle accelerator magnets. High critical current density (J c ) is a key parameter for such applications. Significant efforts towards optimization of various factors led to an 80% improvement in J c from the early 1990s to 2003, when the 4.2 K, 12 T non-matrix J c reached 3000 A/mm 2 (corresponding to 5000 A/mm 2 in Nb 3 Sn layer J c ). [1,2] However, further efforts over the past decade have failed to bring about further increase beyond this level, [3,4] leading some researchers to conclude that the J c of conventional Nb 3 Sn strands had reached its maximum. Here, however, by applying an internal oxidation method, we reduce the grain size by a factor of three and nearly double the 12 T J c . In this method, a Nb 3 Sn strand is fabricated with Nb-Zr alloy as starting material; with oxygen supplied properly via an oxide powder, the Zr atoms in the Nb-Zr alloy are internally oxidized, forming fine intra-granular and inter-granular ZrO 2 particles in Nb 3 Sn layer, which effectively refine Nb 3 Sn grain size. At a reaction temperature of 625 °C, grain size down to 20-50 nm (36 nm on average) has been achieved. For this sample the 4.2 K, 12 T Nb 3 Sn layer J c reached 9600 A/mm 2 .

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Influence of heat treatment temperature and Ti doping on low-field flux jumping and stability in (Nb-Ta)₃Sn strands

Cited by 17 publications

References 42 publications

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

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

A review and prospects for Nb₃Sn superconductor development

Internally Oxidized Nb₃Sn Strands with Fine Grain Size and High Critical Current Density

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Influence of heat treatment temperature and Ti doping on low-field flux jumping and stability in (Nb-Ta)3Sn strands

Cited by 17 publications

References 42 publications

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

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

A review and prospects for Nb3Sn superconductor development

Internally Oxidized Nb3Sn Strands with Fine Grain Size and High Critical Current Density

Contact Info

Product

Resources

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Influence of heat treatment temperature and Ti doping on low-field flux jumping and stability in (Nb-Ta)₃Sn strands

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

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

A review and prospects for Nb₃Sn superconductor development

Internally Oxidized Nb₃Sn Strands with Fine Grain Size and High Critical Current Density