Persistent-Current Magnetization of &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{Nb}_{3}\hbox{Sn} $&lt;/tex-math&gt;&lt;/inline-formula&gt; Strands: Influence of Applied Field Angle and Transport Current

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

doi:10.1109/tasc.2014.2375818

Cited by 5 publications

(3 citation statements)

References 13 publications

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“…The shift of the F p (B) curve peak from 0.2B c2 to 0.5B c2 brings not only significant improvement in high-field J c but also remarkable reduction of low-field J c and associated magnetization, because the J c (B) curve is linear as the F p (B) curve peaks at 0.5B c2 -by contrast, as the F p (B) curve peaks at 0.2B c2 , J c increases sharply as field decreases at low fields (4 T). Since magnetization is the driving force for low-field flux jumps and field errors in magnets, decreasing the lowfield J c by shifting the F p (B) curve peak to 0.5B c2 also benefits in improving low-field stability and suppressing the field errors caused by persistent-current magnetization [10,86].…”

Section: Prospects To Improve Pinning Capacitymentioning

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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Section: Prospects To Improve Pinning Capacitymentioning

confidence: 99%

A review and prospects for Nb₃Sn superconductor development

2017

Supercond. Sci. Technol.

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“…Magnetization and magnetic moment are further affected by a transport current in the cable [18][19][20] which is always present in a superconducting magnet. Generally the magnetization decreases in a nonlinear way as the transport current approaches the cable critical current.…”

Section: Coupling Magnetization and Lossmentioning

confidence: 99%

Inter-strand current sharing and ac loss measurements in superconducting YBCO Roebel cables

Majoroš

Sumption

Collings

et al. 2015

Supercond. Sci. Technol.

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A Roebel cable, one twist pitch long, was modified from its as-received state by soldering copper strips between the strands to provide inter-strand connections enabling current sharing. Various DC transport currents (representing different percentages of its critical current) were applied to a single strand of such a modified cable at 77 K in a liquid nitrogen bath. Simultaneous monitoring of I–V curves in different parts of the strand as well as in its interconnections with other strands was made using a number of sensitive Keithley nanovoltmeters in combination with a multi-channel high-speed data acquisition card, all controlled via LabView software. Current sharing onset was observed at about 1.02 of strand Ic. At a strand current of 1.3Ic about 5% of the current was shared through the copper strip interconnections. A finite element method modeling was performed to estimate the inter-strand resistivities required to enable different levels of current sharing. The relative contributions of coupling and hysteretic magnetization (and loss) were compared, and for our cable and tape geometry, and at dB/dt = 1 T s−1, and our inter-strand resistance of 0.77 mΩ, (enabling a current sharing of 5% at 1.3Ic ) the coupling component was 0.32% of the hysteretic component. However, inter-strand contact resistance values of 100–1000 times smaller (close to those of NbTi and Nb3Sn based accelerator cables) would make the coupling components comparable in size to the hysteretic components.

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“…Accelerator cables and hence magnets exhibit (i) dynamic magnetization, Mcoup, produced by interstrand coupling currents (ISCCs) [3], [4]; and (ii) static, or hysteretic, magnetization, Mh, resulting from strand-based persistent currents [3], [5], [6]. These magnetizations create bore field distortions expressible in terms of normal and skew harmonics bn and an, respectively.…”

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confidence: 99%