Fabrication and Evaluation of High-Tc Superconductor Cables Designed by Using the Novel Calculation Method of AC Transport self-field Losses

1.通过引入阻挡层降低银护套Bi2223带材的交流传输损耗我们成功地降低了77K时的交流传输损耗，这种方法是用四辊机器进行矩形变形，并通过引入Bi2201薄片作为与带材宽表面平行排列的阻挡层。虽然造成损耗的主要原因是超导体的磁滞损耗，但与没有阻挡层的标准粉末法制备的多芯带材相比，带材的损耗值降低了约70%。然而，由于Bi2201薄片在热处理过程中与Bi2223丝发生了一定的反应，临界电流密度(J_C)远低于没有阻挡层的标准带材。为了解决这一问题，我们引入了Ca_2CuO_3和30wt.%Bi2212粉末的混合物作为…更多的障碍。Ca_2CuO_3粉末对Bi2223带材的J_c影响不大。实验结果表明，在平行于带材宽表面的方向上引入阻性势垒可以降低输运损失，而J_c值与未加阻挡层的带材相比几乎没有恶化。银护套Bi2223多芯带材的交流输运损耗在77K的自场中得到显著的降低。这一成就不是由于引入了阻性屏障，而是由于改进了磁带中的灯丝排列。尽管损耗的主要来源是超导体的磁滞损耗，但与标准凹坑工艺制备的Bi2223多芯带材相比，带材样品的输运损耗降低了50-70%，特别是在接近临界电流(Ic)的大电流范围。数值计算表明，传输损耗的降低主要归因于在交流电流传输下，在靠近磁带边缘的分段灯丝组中，没有电流也没有电磁场的无磁场磁芯的分裂。超导带股组成的电缆导体交流输运损耗的评估我们研究了不同截面几何形状的银套Bi2223带股组成的电缆导体在自场中的交流输运损耗。导体的损耗值强烈地取决于带股中的灯丝排列和带股在导体中的排列。这可以用电流分布和损耗密度分布的计算结果来解释，这些分布随导体的几何系数而变化。以螺旋长度为参数，计算了多层电缆中磁场分布在I_o=I_c条件下的层间磁通量。调整螺旋长度后，虽然层间磁通值变为零，但磁带中心和边缘之间的磁通呈现非零值，表明调整螺旋长度的电缆的传输损耗主要产生在磁带股的边缘部分。因此，在实际磁场结构中有很大的改进空间来抑制电缆中的损耗产生。较少

1. Reduction in AC transport losses for Ag-sheathed Bi2223 tapes by introduction of resistive barriersWe succeeded in reducing AC transport losses in self-Held at 77 K for the Ag-sheathed Bi2223 tapes, fabricated by a four-roller machine to make a rectangular deformation and also by the introduction of Bi2201 sheets as resistive barriers in an arrangement parallel to the wide surface of tapes. Although the main contribution to the losses comes from the hysteresis loss of the superconductor, the loss value for the tape is reduced by approximately 70% compared with the value for the multifilamentary tapes prepared by a standard powder-in-process without the resistive barriers. However, the critical current densities (J_c) are much lower than that for the standard tape without the resistive barriers because of the some reaction of Bi2201 sheets with Bi2223 filaments during the heat treatments. To solve this problem, we introduced the mixture of Ca_2CuO_3 and 30 wt.% Bi2212 powders as resi … More stive barriers. The Ca_2CuO_3 powder is has little side effect on the J_c values of the Bi2223 tapes. The experimental results indicate that the transport losses were reduced by introduction of the resistive barrier in an arrangement parallel to the wide surface of tapes, while the J_c value was almost not deteriorated compared with the tape without barriers.2. Reduction in AC transport losses for Ag-sheathed Bi2223 tapes by changing the filament arrangementsSignificant reduction in AC transport losses in self-field at 77 K has been achieved to Ag-sheathed Bi2223 multifilamentary tapes, which were fabricated by a rectangular deformation process using a two-axial rolling (TAR). This achievement is not made by the introduction of resistive barriers but the improvements of filament arrangements in the tapes. Despite the main contribution to the losses comes from the hysteresis loss of the superconductor, the transport losses for the tape samples are decreased by 50-70% particularly in high current range near the critical current (I_c) compared with the value for the Bi2223 multifilamentary tapes prepared by standard PIT process. Numerical calculations suggest that the reduction of transport losses mainly ascribed to the division of field-free core with neither currents nor electromagnetic field in the sectioned filament groups near the tape edge under AC current transmission.3. Evaluation of AC transport losses for cable conductors composed of superconductor tape strandsWe investigated the AC transport losses in self-field on cable conductor composed of Ag-sheathed Bi2223 tape strands with different cross sectional geometry. The loss values of the conductors strongly depend on the filament arrangements in the tape strands and the arrangement of tape strands in the conductors. This can be explained the calculation result of current distributions and loss density distributions, varying with the geometrical factor of conductors. We also calculated the inter-layer magnetic flux under the condition of I_o=I_c for the magnetic field distributions in multi-layer cables as a parameter of spiral length. Although the value of inter-layer flux becomes zero in an adjusted spiral length, the flux between tape center and edges shows non-zero values, indicating that the transport losses for the cables with adjusted spiral length are mainly generated in the edge part of tape strands. Therefore, there is much room for further improvement in actual magnetic field structure to suppress the loss generation in the cables. Less