TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)
Online ISSN : 1880-0408
Print ISSN : 0389-2441
ISSN-L : 0389-2441
Current issue
Displaying 1-6 of 6 articles from this issue
  • Shinsaku IMAGAWA
    2024 Volume 59 Issue 3 Pages 114-122
    Published: May 20, 2024
    Released on J-STAGE: May 20, 2024

    NbTi conductors for helical coils of the Large Helical Device were developed to satisfy cold-end stability. Their recovery currents were measured with a conductor test facility with 9 T split coils at the National Institute for Fusion Science. The measured recovery currents were higher by 15 to 20 % than that calculated from Maddockʼs equal area theorem with the measured conductor resistance and heat transfer. We have proposed an analytical method to estimate the recovery current in a finite magnetic field using the temperature distribution that is calculated with representative thermal conductivity, resistivity, and heat transfer. In order to check the validity of this method, we carried out simulation with a finite-difference method. The results revealed that the proposed analytical method is applicable with slight underestimation as long as the resistivity can be fitted by a function of temperature only. In addition, the necessary length of the magnetic field higher than 95 % is around three times of the temperature characteristic length of the conductor for measurement of recovery currents with an overestimation of less than 5 %.

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  • Yangbo DONG, Satoshi UENO, Mochimitsu KOMORI, Kenichi ASAMI
    2024 Volume 59 Issue 3 Pages 123-128
    Published: May 20, 2024
    Released on J-STAGE: May 20, 2024

    Currently, vacuum robot hands are used to transport semiconductor wafers in vacuum equipment, and vibration suppression methods using feedback control are utilized. Using superconducting (SC) levitation allows non-contact transfer, which reduces disturbances to the wafer, and is expected to reduce vibrations caused by starting, stopping, and loading the wafer. However, a single cylindrical superconducting bulk is insufficient for the damping and stiffness of a floating body and it is thought that it is necessary to further suppress vibrations for the nanomanufacturing process. Therefore, this research proposes a new magnetic support structure that uses a permanent magnet, four superconducting bulks, and four superconducting coils to transport wafers, and to clarify the damping and stiffness in the horizontal and vertical directions through actual measurements. Finally, compared with the case without coils, the damping coefficient was 3.4 times higher, and the spring coefficient was 2.2 times higher.

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Focused Reviews
  • Minoru MAEDA, Jung Ho KIM, Seyong CHOI
    2024 Volume 59 Issue 3 Pages 129-136
    Published: May 20, 2024
    Released on J-STAGE: May 20, 2024

    Multi-band MgB2 materials have been considered and developed for medical and energy applications. Since some of these applications require kilometers-long wires or tapes, many companies have developed MgB2 materials with fabrication processes through powder filling (e.g., a powder-in-tube process), which can satisfy the requirements of the long lengths for commercial production. These material structures have also been studied to enhance the transport performance of the critical current in magnetic fields. For in-field enhancement, it is essential to gain a deep understanding of crystallinity/disorder (which is related to grain growth, the number of defects, and the distribution of strain/distortion). The material crystallinity, which affects the in-field performance, can become anisotropic due to the structural nature of MgB2, but most studies have not focused on this anisotropy. Therefore, this review highlights and discusses multi-band MgB2 materials in terms of critical current performance and anisotropic crystallinity. This perspective can also be useful for further modifying the material structures of wires, tapes, bulks, powders, etc.

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