No-insulation high temperature superconductor (HTS) stack coils show both increased thermal and electrical stability, and present a simplified geometry for the integration of demountable joints. Demountability is a desirable feature for many superconducting applications including fusion magnets, which motivate this research. In this work, a novel vacuum pressure impregnation (VPI) solder process was developed to couple superconducting paths via a low resistance, mechanically simply, demountable joint for a non-insulated coil design. The three low temperature solders considered were In52Sn48 (mp = 118  ∘ C), In100 (mp = 156.6  ∘ C), and Ga100 (mp = 29.8  ∘ C), all with a lower melting point than the Pb37Sn63 (mp = 183  ∘ C) used to solder the HTS tapes into the coil, thus allowing for the advantages of solder in the joint, yet facilitating demountability without disturbing the primary solder in the non-insulated coil stack. A multidisciplinary campaign was undertaken to design, build, test and identify the major challenges with these small-scale demountable solder joints. A multi probe voltage tap system was used to infer the effective resistances to exit a superconducting stack, cross the solder layer, and enter the second superconducting stack, at 77 K. The experimental resistivities show good agreement with a newly developed finite element model that breaks down domains to the level of individual layers of an HTS tape. When taking into account the thermal degradation that can occur to the HTS stacks during the VPI processes, the normalized joint resistances are found to be 528, 668, and 671  nΩcm2 for the In100 , In52Sn48 and Ga100 solders, respectively. The benchmarked finite element model is used to predict normalized joint resistivities for fusion-relevant temperatures and magnetic fields using a 100 µm solder layer thickness, finding 38, 125, and 103 nΩcm2 for the respective solders; these results are competitive with the lowest resistance cable joints presented in the literature.

中文翻译：

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真空压力浸渍非绝缘超导线圈可拆卸焊点性能

无绝缘高温超导 (HTS) 堆叠线圈显示出更高的热稳定性和电稳定性，并为可拆卸接头的集成提供了简化的几何结构。可拆卸性是许多超导应用（包括聚变磁体）的理想特性，这推动了这项研究。在这项工作中，开发了一种新颖的真空压力浸渍（VPI）焊接工艺，通过低电阻、机械简单、可拆卸的接头耦合超导路径，用于非绝缘线圈设计。考虑的三种低温焊料是 我n52Sn48 （议员= 118  ∘ C）， 我n100 （议员= 156.6  ∘ C），和 GA100 （议员= 29.8  ∘ C) 的熔点均低于 磷乙37Sn63 （议员= 183  ∘ C) 用于将 HTS 带焊接到线圈中，从而发挥接头中焊料的优点，同时在不干扰非绝缘线圈堆叠中的主要焊料的情况下促进可拆卸性。我们开展了一项多学科活动来设计、构建、测试和确定这些小型可拆卸焊点的主要挑战。使用多探针电压抽头系统来推断在 77 K 温度下离开超导叠层、穿过焊料层并进入第二个超导叠层的有效电阻。实验电阻率与新开发的有限元模型表现出良好的一致性，该模型打破了将域降低到 HTS 磁带各个层的级别。当考虑到 VPI 工艺期间 HTS 电堆可能发生的热退化时，归一化接头电阻为 528、668 和 671  nΩC米2 为了 我n100 , 我n52Sn48 和 GA100 分别是焊料。基准有限元模型用于预测聚变相关温度和磁场的归一化接头电阻率，使用 100 µm 焊料层厚度，结果为 38、125 和 103 nΩC米2 对于相应的焊料；这些结果与文献中提出的最低电阻电缆接头具有竞争力。