Reversible and irreversible effects of strain on the critical current density of a niobium–tin superconducting wire

Taylor, David M J; Keys, Simon A; Hampshire, D.P.

doi:10.1016/s0011-2275(02)00009-7

Cited by 9 publications

(8 citation statements)

References 11 publications

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“…This was to ensure that both tensile and compressive data were obtained before applying the large compressive strains that cause strong plastic deformation of some components of the wire. J C at zero applied strain was generally found to be reversible after the tensile strain cycle to within ∼1%, in agreement with previous strain cycling results [48,49].…”

Section: Samplessupporting

confidence: 91%

Properties of helical springs used to measure the axial strain dependence of the critical current density in superconducting wires

Taylor

Hampshire

2005

Supercond. Sci. Technol.

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The use of helical (Walters) springs is an effective technique for measuring the critical current density (J C ) of superconducting wires in high fields as a function of both compressive and tensile axial strains. We report J C versus strain measurements for Nb 3 Sn wires on a number of helical springs of different materials and geometries, together with results from finite element analysis (FEA) of these systems. The critical current density, n-value and effective upper critical field data are universal functions of intrinsic strain (to within ±5%) for measurements on four different spring materials. The strains on the wire due to the differential thermal contraction of the spring are equivalent to the applied mechanical strains and hence only produce a change in the parameter ε M (the applied strain at the peak in J C ). Variable-strain J C data for springs having turns with rectangular and tee-shaped cross-sections (and hence different transverse strain gradients across the wire) show good agreement when the strain-gauge calibration data are corrected to give the strain at the midpoint of the wire. The correction factors can be obtained from FEA or analytical calculations. Experimental and FEA results show that the applied strain varies periodically along the wire with an amplitude that depends on the spring material and geometry. We suggest that Ti-6Al-4V springs with an integer number of turns and optimized tee-shaped cross-sections enable highly accurate measurements of the intrinsic properties of superconducting wires.

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Section: Samplessupporting

confidence: 91%

Properties of helical springs used to measure the axial strain dependence of the critical current density in superconducting wires

Taylor

Hampshire

2005

Supercond. Sci. Technol.

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“…In these types of tapes, the strain dependence of both twinned domains is similar so, as with Bi 2 Sr 2 Ca 2 Cu 3 O x conductors which also have unimodal strain behaviour of J c ( ε ) 54 , there is no competition between the domains 32,55 and it leads to a weak monotonic strain dependence for J c . There is also additional evidence in the literature for bimodal behaviour in other LTS materials as evidenced by the double-valued behaviour of 56 .…”

Section: Discussionmentioning

confidence: 88%

Weakly-Emergent Strain-Dependent Properties of High Field Superconductors

Branch

Tsui

Osamura

et al. 2019

Sci Rep

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All superconductors in high field magnets operating above 12 T are brittle and subjected to large strains because of the differential thermal contraction between component parts on cool-down and the large Lorentz forces produced in operation. The continuous scientific requirement for higher magnetic fields in superconducting energy-efficient magnets means we must understand and control the high sensitivity of critical current density Jc to strain ε. Here we present very detailed Jc(B, θ, T, ε) measurements on a high temperature superconductor (HTS), a (Rare−Earth)Ba2Cu3O7−δ (REBCO) coated conductor, and a low temperature superconductor (LTS), a Nb3Sn wire, that include the very widely observed inverted parabolic strain dependence for Jc(ε). The canonical explanation for the parabolic strain dependence of Jc in LTS wires attributes it to an angular average of an underlying intrinsic parabolic single crystal response. It assigns optimal superconducting critical parameters to the unstrained state which implies that Jc(ε) should reach its peak value at a single strain (ε = εpeak), independent of field B, and temperature T. However, consistent with a new analysis, the high field measurements reported here provide a clear signature for weakly-emergent behaviour, namely εpeak is markedly B, (field angle θ for the HTS) and T dependent in both materials. The strain dependence of Jc in these materials is termed weakly-emergent because it is not qualitatively similar to the strain dependence of Jc of any of their underlying component parts, but is amenable to calculation. We conclude that Jc(ε) is an emergent property in both REBCO and Nb3Sn conductors and that for the LTS Nb3Sn conductor, the emergent behaviour is not consistent with the long-standing canonical explanation for Jc(ε).

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“…However, the functional form will have reduced utility either if an unreasonably large range of measurements are required to find the free parameters or if there are so many free (correlated) parameters that the best fits give meaningless constants which are, for example, very sensitive to small changes in the range over which the data are fitted. In the latter context we suggest that the previous data sets for bronze-route Nb 3 Sn [14,15], jelly-roll Nb 3 Sn [21,22] and Nb 3 Al [16] can be parameterized making the assumption that m = 2 without losing significant accuracy. If we assume that the scaling law has the form of equation ( 5) where A * is a constant and that the expression for κ (equation ( 9)) is valid, then the scaling analysis (figure 10) demonstrates that m = 2 provides the best fit.…”

Section: C2mentioning

confidence: 99%

“…Furthermore, regardless of how much (or even whether) the scaling laws are properly understood, the engineering community has continued developing superconducting magnets for cryocooled systems, particle accelerators and Tokamaks [19]. Our group has put significant effort into obtaining comprehensive J E (B, T, ε) data for a range of A15 superconducting strands [14][15][16][20][21][22]. These data are required to model and optimize the design of magnet systems.…”

Section: Introductionmentioning

confidence: 99%

A scaling law for the critical current density of weakly- and strongly-coupled superconductors, used to parameterize data from a technological Nb₃Sn strand

Keys

Hampshire

2003

Supercond. Sci. Technol.

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There is currently no consensus on how best to parameterize the large volume of data produced in measuring the magnetic field (B), temperature (T) and strain (ε) dependence of the engineering critical current density (JE(B, T, ε)) for A15 superconducting strands. For the volume pinning force (FP) and the upper critical field BC2(T, ε), we propose given b = B/BC2(T, ε) and t = T/TC(ε) where TC(ε) is the critical temperature. FP (or JE(B, T, ε)) includes three strain-dependent variables α(ε), BC2(0, ε) and TC(ε) and four constants, n, p, q and v. The form is different to that proposed by Summers et al by a factor T2C(ε). We suggest that the form is sufficiently general to describe superconductors whether the electron–phonon coupling is weak or strong and find that α(ε) is proportional to where Δ(ε) is the superconducting gap and γ(ε) is the Sommerfeld constant. Comprehensive JE(B, T, ε) data are presented for a modified jelly-roll (MJR) Nb3Sn conductor that are consistent with the form proposed with n ≈ 5/2, p = ½, q = 2 and v = 1.374. Hence the scaling law proposed leads to a critical current density for the MJR Nb3Sn given by Comparison with data in the literature suggests that α(ε) ≈ 3 × 10−3μ0γ(ε). Furthermore, the volume pinning force (FP(S/C)) within the Nb3Sn superconducting filaments alone can be described in terms of superconducting parameters in the form where κ(T, ε) is the Ginzburg–Landau parameter.

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Reversible and irreversible effects of strain on the critical current density of a niobium–tin superconducting wire

Cited by 9 publications

References 11 publications

Properties of helical springs used to measure the axial strain dependence of the critical current density in superconducting wires

Properties of helical springs used to measure the axial strain dependence of the critical current density in superconducting wires

Weakly-Emergent Strain-Dependent Properties of High Field Superconductors

A scaling law for the critical current density of weakly- and strongly-coupled superconductors, used to parameterize data from a technological Nb₃Sn strand

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Reversible and irreversible effects of strain on the critical current density of a niobium–tin superconducting wire

Cited by 9 publications

References 11 publications

Properties of helical springs used to measure the axial strain dependence of the critical current density in superconducting wires

Properties of helical springs used to measure the axial strain dependence of the critical current density in superconducting wires

Weakly-Emergent Strain-Dependent Properties of High Field Superconductors

A scaling law for the critical current density of weakly- and strongly-coupled superconductors, used to parameterize data from a technological Nb3Sn strand

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A scaling law for the critical current density of weakly- and strongly-coupled superconductors, used to parameterize data from a technological Nb₃Sn strand