[论文解读] Stable, predictable operation of racetrack coils made of high-temperature superconducting Bi-2212 Rutherford cable at the very high wire current density of more than 1000 A/mm2

Tengming Shen, Jianyi Jiang+15 more|arXiv (Cornell University)|Aug 8, 2018

Superconducting Materials and Applications被引用 2

一句话总结

本论文展示了使用纳米喷雾处理的多芯线材绕制的17股Rutherford电缆制造的Bi-2212跑道线圈在稳定、无淬火状态下的运行，实现了4.2 K下950 A/mm²的记录性线材电流密度，并在3.5 T下维持8.6 kA电流，线材电流密度达1020 A/mm²，表现出超过1米的高场区域中可预测、均匀的淬火行为，实现了可靠、无需训练淬火的性能，优于Nb-Ti或Nb3Sn磁体。

ABSTRACT

High-temperature superconductors (HTS) could enable high-field magnets much stronger than is possible with Nb-Ti and Nb3Sn, but two key limiting factors have so far been the difficulty of achieving high critical current density in long-length conductors, especially in high-current cables, and the danger of quenches out of the superconducting into the normal state. Here we demonstrate stable, reliable and training-quench-free performance of Bi-2212 racetrack coils wound with a 17-strand Rutherford cable fabricated from wires made with nanospray Bi-2212 powder. These multifilament wires are now being delivered in single lengths of more than 1 km with a new record whole-wire critical current density up to 950 A/mm2 at 30 T at 4.2 K. These coils carried up to 8.6 kA while generating a peak field of 3.5 T at 4.2 K, at a wire current density of 1020 A/mm2. Quite different from the unpredictable training performance of Nb-Ti and Nb3Sn magnets, these Bi-2212 magnets showed no training quenches and entered the flux flow state in a stable manner before thermal runaway and quench occurred. Also quite different from Nb-Ti, Nb3Sn, and REBCO magnets for which localized thermal runaways occur at unpredictable locations, the quenches of Bi-2212 magnets consistently occurred in the high field regions over a conductor length greater than one meter. These characteristics make quench detection rather simple, enabling safe protection, and suggest a new paradigm of constructing quench-predictable superconducting magnets from Bi-2212, which is, like Nb-Ti and Nb3Sn, isotropic, round, multifilament, uniform over km lengths and suitable for Rutherford cable use but, unlike them, much more tolerant of the energy disturbances that often lead Nb-based superconducting magnets to premature quench and long training cycles.

研究动机与目标

• 为克服高温超导体（HTS）在长长度、大电流电缆中实现高临界电流密度的局限性。
• 解决Nb-Ti和Nb3Sn磁体在训练和运行过程中出现的不稳定性和不可预测的淬火行为。
• 开发一种基于Bi-2212 Rutherford电缆的可预测淬火、稳定超导磁体设计，适用于高场应用。
• 展示在超过1000 A/mm²的线材电流密度下实现可靠、无需训练淬火的性能。
• 利用各向同性、圆形、多芯Bi-2212线材实现安全、可扩展的磁体结构，该线材与Rutherford电缆技术兼容。

提出的方法

• 通过纳米喷雾粉末工艺制备的多芯Bi-2212线材，制造17股Rutherford电缆。
• 使用Rutherford电缆绕制跑道线圈，并在4.2 K下高电流和高场条件下进行测试。
• 在30 T和4.2 K下测量整根线材的临界电流密度，以评估性能极限。
• 在升流和降流过程中监测淬火行为，以评估稳定性和可预测性。
• 分析淬火位置和传播特性，以确定空间一致性及可检测性。
• 与Nb-Ti、Nb3Sn和REBCO磁体的淬火特性进行对比，突出其在可预测性及失效模式上的差异。

实验结果

研究问题

• RQ1 Bi-2212 Rutherford电缆是否能在超过1000 A/mm²的线材电流密度下实现稳定、无需训练淬火的运行？
• RQ2 Bi-2212磁体中的淬火行为是否表现出一致的空间定位性，从而实现可靠的淬火检测？
• RQ3 Bi-2212磁体的淬火起始行为与Nb-Ti和Nb3Sn磁体中常见的局部化、不可预测的热失控相比有何不同？
• RQ4 在4.2 K和30 T条件下，长长度Bi-2212多芯线材可实现的最大线材电流密度是多少？
• RQ5 Bi-2212磁体能否被设计为在高场应用中可靠运行，且无需漫长的训练周期？

主要发现

• Bi-2212 Rutherford电缆在4.2 K和30 T下实现了950 A/mm²的记录性整根线材临界电流密度。
• 线圈在4.2 K下维持8.6 kA电流，产生3.5 T的峰值磁场，线材电流密度达1020 A/mm²。
• 未观察到训练淬火，表明无需长时间训练周期，运行稳定可靠。
• 淬火在超过一米长的高场区域中一致发生，实现了可预测的检测。
• 淬火行为均匀且可预测，与Nb-Ti和Nb3Sn磁体中局部化、不可预测的热失控形成鲜明对比。
• Bi-2212线材的各向同性、圆形、多芯特性使其在Rutherford电缆结构中表现稳定，适用于可扩展的磁体制造。