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 49, Issue 2
Displaying 1-6 of 6 articles from this issue
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Preface
Review Article
Originals
  • Fabrication and Temperature Dependence of Jc of Tl-1223 Films on Ag Substrates using a Laser Ablation Process
    Junichi SATO, Sumio HOSAKA
    2014 Volume 49 Issue 2 Pages 54-61
    Published: February 25, 2014
    Released on J-STAGE: March 18, 2014
    DOIhttps://doi.org/10.2221/jcsj.49.54
    JOURNAL FREE ACCESS
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    We prepared polycrystalline Tl-1223 films without impurity phases and with a c-axis orientation by heat treatment and intermediate pressing of precursor films using a laser ablation process on Ag substrates. The critical temperature (Tc) of Tl1223 films on Ag was 120 K and the critical current density (Jc) was 15 kA/cm2 at 77 K, 0 T. The strong field dependence of Jc of the Tl-1223 films in a low magnetic field showed that the grain boundaries of the Tl-1223 films behaved like a weak link. The temperature dependence of Jc of the Tl-1223 films was proportional to (1-T/Tc)n with n=2.0 for 0.08 ?? 1-T/Tc ?? 0.38. These results confirm that grain boundaries in Tl-1223 films act as superconductor-normal metal-superconductor (SNS) junctions.
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  • Characterization of Ag-Sheathed Bi2223 Tapes with Interfilamentary Oxide Barriers AC Loss Reduction under AC Perpendicular Transverse Magnetic Field
    Ryoji INADA, Yasuhiro OKUMURA, Ryosuke OHTSU, Akio OOTA
    2014 Volume 49 Issue 2 Pages 62-68
    Published: February 25, 2014
    Released on J-STAGE: March 18, 2014
    DOIhttps://doi.org/10.2221/jcsj.49.62
    JOURNAL FREE ACCESS
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    Low AC loss Ag-sheathed Bi2223 tapes with oxide barriers among the twisted filaments were successfully fabricated using the powder-in-tube method. SrZrO3 was selected as the barrier material for its compatibility with Bi2223 oxide. Moreover, a small amount of Bi2212 was mixed with SrZrO3 to improve its ductility for cold working. By controlling barrier thickness and reducing the final tape width down to 2.7 mm, transport critical current densities Jc at 77 K and self-field attained 17-23 kA/cm2 for twisted barrier tapes with twist lengths Lt between 4 and 9 mm. For barrier tape with the shortest Lt = 4 mm, a coupling frequency fc , which is related to inverse of coupling time constant &tau;c, of 270 Hz was attained in an AC transverse field perpendicular to a broader face of the tape. To our best knowledge, fc = 270 Hz under a perpendicular field is the highest ever reported value for Bi2223 tapes with self-field Jc > 15 kA/cm2 at 77 K. According to these achievements, perpendicular field losses around 50 Hz for barrier tape were 70-80% lower than those for conventional 4 mm-width tape with fully coupled filaments.
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  • Optimization of External-heating-type MgB2 Level Sensor for Liquid Hydrogen
    Kazuma MAEKAWA, Minoru TAKEDA, Yu MATSUNO, Shizuichi FUJIKAWA, Tsuneo ...
    2014 Volume 49 Issue 2 Pages 69-75
    Published: February 25, 2014
    Released on J-STAGE: March 18, 2014
    DOIhttps://doi.org/10.2221/jcsj.49.69
    JOURNAL FREE ACCESS
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    We are currently developing an external-heating-type superconducting magnesium diboride (MgB2) level sensor for a liquid hydrogen tank. The heating effect of an external heater on an 800-mm-long MgB2 level sensor was previously reported. However, the heating effect of an external heater on the MgB2 level sensor has not yet been clarified in the case of changing the sensor length. In this study, we examined the temperature distribution and level-detecting characteristics of a 200- mm-long MgB2 level sensor. It was found that the temperature of the sensor above the liquid surface was higher than Tc at a heater input of 6 W or more. Regarding the level-detecting characteristics of the MgB2 sensor, the linear correlation coefficient was 0.99 or more at a heater input of 3 W and above. Moreover, the ratio of the effective level-detecting length to the total length remained constant at a heater input of 6 W or more. Similar results were observed for different sensor lengths. Therefore, the optimum heater input was 6 W regardless of the sensor length.
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Cryogenic Group
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