Journal of Advanced Science
Online ISSN : 1881-3917
Print ISSN : 0915-5651
ISSN-L : 0915-5651
21 巻 , 1+2 号
選択された号の論文の9件中1~9を表示しています
Paper
  • Yusuke KIMURA, Masaki KUBOTA, Shigehito OHKI, Kei SHIOHARA, Satosh ...
    2009 年 21 巻 1+2 号 p. 1-4
    発行日: 2009年
    公開日: 2009/07/07
    ジャーナル フリー
    Superconductive current lead has been prepared by the TFA-MOD processed YBCO tapes. That is composed of 12 YBCO tapes having critical current (Ic) of around 100 A at 77 K. The tapes are 4.5 mm in width, 200 mm in length and about 120 μm in thickness. The 1 μm thick superconductive YBCO layer is formed on HastelloyTM substrate tape with buffer oxide layers through the TFA-MOD process. The 12 YBCO tapes are arrayed on the both sides (6 tapes on one side) of the stainless steel board with 3mm in thickness for a board type. They are similarly soldered to copper caps at the both ends.The transport current of 1,000 A was stably applied for 10 minutes 77K without any voltage. The transport current of 1,200 A was successfully applied without quenching. The voltage between both copper caps linerly increased with increasing the transport current, and it was about 300μV at the applied currents of 1,000A. The overall thermal conductivity of the current lead composed of YBCO tapes and stainless steel board is much lower than that of non-superconducting current leads. Therefore, the present current lead with small heat leakage seems to be practically promising for superconducting magnets.
Paper
Paper
  • Masahiro SHIMOZAWA, Koji NAGADOME, Yutaka NEMOTO, Sigehito OHKI, Y ...
    2009 年 21 巻 1+2 号 p. 9-12
    発行日: 2009年
    公開日: 2009/06/26
    ジャーナル フリー
    MgB2 superconducting thin wires have been prepared by in-situ powder-in-tube process. Using Magnesium hydride MgH2 and amorphous B powders with SiC nano-sized powder addition, SS/Fe/MgB2/ steel composite wires of 0.53 mm ∼ 0.19 mm in diameter have been fabricated through grooved rolling and drawing. The stainless steel sheath was hardened to a Vickers hardness of around 600 Hv by cold drawing. The Ic at 4.2 K and self-field for the MgB2 wire of 0.53 mm in diameter without SiC addition is 200 A, which corresponds to the critical current density (Jc) of 4,300 A/mm2. The MgB2 composite thin wires sheathed with low thermal conductive metals are promising as current leads with small heat leakage in liquid hydrogen.
Paper
Paper
  • -温度時系列データのフラクタル次元-
    Hiroyuki NISHIKAWA, Shigeki OKINO, Fujio SUDA
    2009 年 21 巻 1+2 号 p. 20-26
    発行日: 2009年
    公開日: 2009/07/24
    ジャーナル フリー
    An experimental investigation has been made on the flow in a natural convection loop. Time series data of temperature oscillation were obtained for various types of the flow. Based on these data, attractors in high-dimensional space have been reconstructed by obtaining optimum delay time. The correlation dimensions Dc for these attractors were calculated by the method of correlation integration and plotted against heat inputs. The values of Dc could be classified into three regions according to the value of heat flux q, 1) Dc ≥ 13 in the laminar region (q ≤ 4.13kW/m2), 2) 1.1 ≤ Dc ≤ 2.4 in the unstable region (5.51 ≤ q ≤ 22.0), and 3) Dc ≥ 11.5 in the turbulent region (q ≥ 23.4). The values of Dc are non-integer in all regions. These results are consistent with chaotic characteristics. Observed in detail, however, the region 2) contains three types of flows: Turbulent, unstable with and without flow reversals. The last one was considered to be unstable flow in spite of non-reversal, because of its small Dc.
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