Characteristics of Distributed Tin Nb3Sn Conductor

Egawa, Kunihiko; Kubo, Yukihiro; Nagai, Takashi; Sone, Takanori; Hiramoto, Kiyoshi; Taguchi, Osamu; Kitakoga, H.; Wake, M.; Shintomi, T.; Nakayama, Shinya

doi:10.1063/1.1774595

Cited by 11 publications

(2 citation statements)

References 3 publications

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“…The line is provided by the Durham scaling law for the BEAS II data. 33,35] and that some heat treatments lead to crossover behavior of J c at high magnetic fields that can even occur at zero applied strain-observed in both bronze-route and internal-tin wires [27,[43][44][45][46]. Part of the difficulty results from untangling the role of the many different features of the final form of the bronze-route and internal composite strands.…”

Section: Discussionmentioning

confidence: 99%

Critical current scaling and the pivot-point in Nb₃Sn strands

Tsui¹,

Hampshire²

2012

Supercond. Sci. Technol.

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Detailed measurements are provided of the engineering critical current density (J c) and the index of transition (n-value) of two different types of advanced ITER Nb 3 Sn superconducting strand for fusion applications. The samples consist of one internal-tin strand (OST) and two bronze-route strands (BEAS I and BEAS II-reacted using different heat treatments). Tests on different sections of these wires show that prior to applying strain, J c is homogeneous to better than 2% along the length of each strand. J c data have been characterized as a function of magnetic field (B ≤ 14.5 T), temperature (4.2 K ≤ T ≤ 12 K) and applied axial strain (−1% ≤ ε A ≤ 0.8%). Strain-cycling tests demonstrate that the variable strain J c data are reversible to better than 2% when the applied axial strain is in the range of −1% ≤ ε A ≤ 0.5%. The wires are damaged when the intrinsic strain (ε I) is ε I ≥ 0.55% and ε I ≥ 0.23% for the OST and BEAS strands, respectively. The strain dependences of the normalized J c for each type of strand are similar to those of prototype strands of similar design measured in 2005 and 2008 to about 2% which makes them candidate strands for a round-robin interlaboratory comparison. The J c data are described by Durham, ITER and Josephson-junction parameterizations to an accuracy of about 4%. For all of these scaling laws, the percentage difference between the data and the parameterization is larger when J c is small, caused by high B, T or |ε I |. The n-values can be described by a modified power law of the form n = 1 + rI s c , where r and s are approximately constant and I c is the critical current. It has long been known that pivot-points (or cross-overs) in J c occur at high magnetic field and temperature. Changing the magnetic field or temperature from one side of the pivot-point to the other changes the highest J c sample to the lowest J c sample and vice versa. The pivot-point follows the B-T phase boundary associated with the upper critical field and is usually attributed to the different tin content profiles and pinning properties of internal-tin and bronze-route strands. We report that the strain dependence of the pivot-point in these strands is quite different from that of the upper critical field and suggest that its origin in optimized high tin content strands is the proximity of the tetragonal Nb 3 Sn phase, which has low superconducting critical parameters.

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Section: Discussionmentioning

confidence: 99%

Critical current scaling and the pivot-point in Nb₃Sn strands

Tsui¹,

Hampshire²

2012

Supercond. Sci. Technol.

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“…No limitation in the Sn content can lead to Nb Sn wires with high properties in these processes. The internal-tin technique is now being developed widely in the world, and wires with high properties have been reported [5]- [7]. We have developed an internal-tin wire which has a simple cross-sectional structure using a simple fabrication process.…”

Section: Introductionmentioning

confidence: 99%

Development of Single-Stacked Internal-Tin Nb$_{3}$Sn Superconducting Wire

Ohata

Miyashita

Wadayama

et al. 2012

IEEE Trans. Appl. Supercond.

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The internal-tin technique is an excellent method of fabricating Nb Sn superconducting wires with high critical current densities. We have developed an internal-tin Nb Sn wire in which the multi-filamentary wire is fabricated by assembling mono-filamentary Nb elements and mono-filamentary Sn elements. The simple fabrication process allows a reduction in the fabrication cost of the wires. By optimizing the spacing of the Nb Sn filaments, a 600 m long wire with a high critical current density of 400 A/mm at 18 T and no flux jumping was fabricated.

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