TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)
Online ISSN : 1880-0408
Print ISSN : 0389-2441
ISSN-L : 0389-2441
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Volume 38, Issue 6
Displaying 1-7 of 7 articles from this issue
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Preface
Originals
  • Thermal Stability of Reinforced Nb3Sn Composite Superconductor under Cryocooled Conditions
    Tsuyoshi YAMAMOTO, Kenji WATANABE, Satoru MURASE, Gen NISHIJIMA, Kazuo ...
    2003 Volume 38 Issue 6 Pages 262-269
    Published: 2003
    Released on J-STAGE: August 26, 2005
    DOIhttps://doi.org/10.2221/jcsj.38.262
    JOURNAL FREE ACCESS
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    Superconducting coils that generate a high magnetic field are subjected to a large electromagnetic force. In general, compound superconductors such as Nb3Sn are sensitive to stress and strain; the superconducting properties for instance, critical current density decrease, as force increases. To prevent a reduction in superconducting properties, several kinds of reinforced Nb3Sn wires have been developed. Reinforced materials such as Cu-Nb, Ta, Alumina-Cu and Nb-Ti-Cu, have been developed. To fabricate a cryocooled magnet using those reinforced wires, we experimentally measured the minimum quench energy (MQE) under the cryocooled conditions of some reinforced Nb3Sn wires. As a result, it became clear that thermal stability expressed as MQE was controlled by the temperature margin between the temperature of the operating condition and the superconductivity to normal transition temperature. Using the FEM analysis, it is realized that cause of the decline in thermal stability at the time of reinforcement was the low thermal conductivity of the reinforce materials.
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  • Analysis of Current Distributions in a Multi-laminated HTS Tape Conductor for Solenoid Coils
    Takataro HAMAJIMA, Naoyuki HARADA, Makoto TSUDA, Takashi YAZAWA, Toru ...
    2003 Volume 38 Issue 6 Pages 270-277
    Published: 2003
    Released on J-STAGE: August 26, 2005
    DOIhttps://doi.org/10.2221/jcsj.38.270
    JOURNAL FREE ACCESS
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    A multi-laminated HTS tape conductor has been recently developed for large coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is imbalanced because of the differences among all tape inductances. Transposition of the tapes in the conductor is effective for homogeneous current distribution, but the tape may be damaged due to the lateral bending. The solenoid coil has enough space to transpose the tapes at both ends. However, a proposed theory so far requires a restriction in the number of coil layers for homogeneous current distribution in the laminated tape conductor. It is very important to analyze current distributions in the multi-laminated tape conductor for the solenoid coil with arbitrary layers. In this paper, we apply the Maxwell integral equation to the region contoured by adjacent laminated tapes to analyze the current distributions of the tapes in an infinite solenoid coil, and demonstrate that the flux across the region is conserved as long as the tapes are not saturated, and finally induce the fundamental equations as functions of coil construction parameters, such as layer radii, laminated tape spaces, and winding pitches. We use the fundamental equations for 2 and 4-layer coils to verify the homogeneous current distribution of the laminated tape conductor for an arbitrary layer number. Since the flux between the tapes in the inner layer of a 2-layer coil is contributed from the outer layers, the tape space in the outer layer must be larger than that in the inner layer because of the balance between the two fluxes. Moreover, we have developed an analysis method for a finite solenoid coil.
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  • Experiment of Current Distributions in a Multi-laminated HTS Tape Conductor for Solenoid Coils
    Takataro HAMAJIMA, He JIFANG, Naoyuki HARADA, Makoto TSUDA, Takashi YA ...
    2003 Volume 38 Issue 6 Pages 278-284
    Published: 2003
    Released on J-STAGE: August 26, 2005
    DOIhttps://doi.org/10.2221/jcsj.38.278
    JOURNAL FREE ACCESS
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    A multi-laminated HTS tape conductor has recently been developed for large coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of the differences among all tape inductances. Transposition of the tape in the conductor is effective for homogeneous current distribution, but the tape may be damaged due to the lateral bending. In our previous paper, we proposed a new theory to analyze and control current distributions in the multi-laminated tape conductor for a solenoid coil with arbitrary layers. We applied the Maxwell integral equation to the region contoured by adjacent laminated tapes to analyze the current distributions of the tapes in the infinite solenoid coil, demonstrated that the flux across the region is conserved as long as the tapes are not saturated, and finally induced fundamental equations as functions of coil construction parameters, such as layer radius, laminated tape space, and winding pitch. In order to verify the theory, we designed two kinds of coils with homogenous and inhomogeneous current distributions in the two-laminated tape conductor by adjusting the space between the tapes in the second layer, and fabricated them. In the case when the space between the tapes in the second layer is the same as that of the first layer, 0.31 mm in thickness, we measured the tape currents of 7:3 for the inner and outer tape of the first layer, respectively. We adjusted the space between the tapes of the second layer, 1.78 mm in thickness, while the space of the first layer remained unchanged, 0.31 mm in thickness. We obtained the homogeneous current distribution in the tape conductor. The experimental data were in good agreement with the theory.
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  • Compact Stranded Superconducting Conductors with both Low AC Loss and High Stability
    I. Proposal of a New Design
    Akifumi KAWAGOE, Fumio SUMIYOSHI, Toshiyuki MITO, Teruko KAWASHIMA, Na ...
    2003 Volume 38 Issue 6 Pages 285-290
    Published: 2003
    Released on J-STAGE: August 26, 2005
    DOIhttps://doi.org/10.2221/jcsj.38.285
    JOURNAL FREE ACCESS
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    A new method for designing compact stranded superconducting conductors is proposed as a solution to the dilemma that low loss and high stability cannot be simultaneously attained in the commonly used conductors. In our design, the twist directions of the conductor and those of the sub-cables in it are the same. In addition, the twist pitch of the sub-cables is relatively longer than that of the conductor. The sub-cables cross over each other in the conductor. Under the changing transverse magnetic fields oriented perpendicular to the broad face of the conductor, the induced voltages between the above-mentioned crossover sub-cables become small, so inter-sub-cable coupling losses are decreased. As a result, not only the total coupling loss in the conductor is decreased, but also high stability is maintained due to the low contact resistance between the sub-cables. Our method theoretically indicates such high performance as attaining both low AC loss and high stability. An example of our design is shown for a large-scale compact stranded superconducting conductor.
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  • Compact Stranded Superconducting Conductors with both Low AC Loss and High Stability
    II. Experiment to Confirm Fundamental Performance
    Akifumi KAWAGOE, Fumio SUMIYOSHI, Toshiyuki MITO, Teruko KAWASHIMA
    2003 Volume 38 Issue 6 Pages 291-298
    Published: 2003
    Released on J-STAGE: August 26, 2005
    DOIhttps://doi.org/10.2221/jcsj.38.291
    JOURNAL FREE ACCESS
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    In our previous paper, we proposed a new method for designing compact stranded superconducting conductors as a solution to the dilemma that low loss and high stability could not be simultaneously attained in commonly used conductors. By adjusting the twist pitches and directions of the sub-cables in the conductor, inter-sub-cable coupling losses in it are decreased. As a result, not only the total coupling loss in the conductor is decreased, but also high stability is maintained due to the low contact resistance between the sub-cables. The fundamental performance of the conductors designed using our method has been confirmed by measuring the coupling loss and the minimum quench energies in the conductor. Our measurements are, in this case, carried out using Rutherford cables with strands instead of the conductors with sub-cables. The results obtained successfully show the validity of our new design method.
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