低温工学
Online ISSN : 1880-0408
Print ISSN : 0389-2441
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39 巻 , 4 号
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研究論文
  • 平川 正澄, 山田 秀之, 熊倉 浩明, 松本 明善, 北口 仁
    39 巻 (2004) 4 号 p. 144-147
    公開日: 2008/03/10
    ジャーナル フリー
    It is necessary to increase the Jc values when developing practical MgB2 superconducting wire. High Jc values even in high magnetic fields were achieved using nanometer-sized Mg powder. The highly pure nanometer-sized Mg powder was fabricated using the thermal plasma method. In addition, doping with a small amount of SiC was tried for the purpose of enhancing Jc properties. The MgB2 superconducting wires were MgB2/Fe tapes prepared from a mixture of nanometer-sized Mg, commercial amorphous B and SiC, which were fabricated using the in-situ PIT method. The Jc values of the non-doped and 10 at% SiC-doped tapes reached 90 and 250 A/mm2 at 4.2 K and 10 T, respectively. In regard to the temperature dependence of Jc, it reached at 160 A/mm2 at 20 K and 4 T which nears the practical application level.
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  • 富永 昭
    39 巻 (2004) 4 号 p. 148-154
    公開日: 2008/03/10
    ジャーナル フリー
    Thermoacoustic pheomena are classified into heat-pumping, prome-mover and dream-pipe including simple heat-conduction. Necessary conditions for thermoacoustic heat-engines are discussed using the first and second laws of thermodynamics and thermoacoustic theory. These conditions restirict possible regions of the temperature gradient and the phase difference between oscillations of pressure and displacement.
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  • 重森 雅直, 内田 智史, 堀井 滋, 下山 淳一, 岸尾 光二
    39 巻 (2004) 4 号 p. 155-160
    公開日: 2008/03/10
    ジャーナル フリー
    A large amount of lead doping to Bi2212 superconductors is effective in decreasing their high electromagnetic anisotropy and introduces effective pinning sites, such as lamella structure interfaces due to compositional fluctuation of lead ions, resulting in greatly enhanced flux pinning properties up to high temperatures. Particularly in the high-Tc superconducting materials with lowered anisotropy, further improvement of critical current properties can be expected by doping a small amount of impurity elements, which generate locally weak superconducting regions. Based on this background, we have attempted to enhance flux pinning strength of Bi(Pb)2212 single crystals by 3d metal doping in the present study. Crystal boules with starting compositions of Bi1.6Pb0.6Sr1.8Ca(Cu1-xMx)2Oy (M = Fe, Co, Ni : x = 0, 0.001, 0.002, 0.005, 0.02) were grown by the floating zone method. Tc's of the single crystals annealed to be the carrier overdoped state were dramatically decreased with an increase of metal doping levels. Critical current performance of the 3d metal-doped Bi(Pb)2212 crystals was quite poor at high temperatures near Tc, The crystal with x= 0.001, 0.002, 0.005, however, showed improved Jc properties accompanied by larger second peak effects in their magnetization hysteresis loops when compared with the 3d metal free Bi(Pb)2212 crystal below 50 K. On the other hand, magneto-optical measurements revealed that anisotropy in the in-plane Jc properties (Jca > Jcb ) was systematically suppressed with an increase of the doping level x. These results suggested that a very small amount of 3d metal doping is an essentially effective method to enhance pinning strength of Bi-based superconductors due to their generation of point-defect-like pinning centers. 3d doping, however, does decrease the pinning strength at the lamella structure interfaces.
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研究ノート
  • 高畑 一也
    39 巻 (2004) 4 号 p. 161-165
    公開日: 2008/03/10
    ジャーナル フリー
    The hotspot temperature is one of the most important design criteria for cable-in-conduit conductors. In general, the amount of copper, as a stabilizer, in a bundle is determined by the allowable hotspot temperature, which contradicts to have a high current density in the conductor. In this study, a conductor with a copper-clad conduit is proposed. Current sharing between the bundle and copper cladding can reduce the current in the bundle during a quench. This reduces the hotspot temperature. The effect of copper cladding is analyzed for simulated conductors using zero-dimensional heat-balance equations. The simulated conductors have a circular cross-section with a diameter of 50 mm and a 1-mm-thick copper cladding outside a stainless-steel conduit. The analyses demonstrate the possibility of reducing the hotspot temperature even though high thermal resistance exists between the bundle and conduit.
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