[论文解读] Racetrack coils made of high-temperature superconducting Bi-2212 Rutherford cable operating in a stable and predictable behavior at >8 kA and a wire current density more than 1000 A/mm2

Tengming Shen, Jianyi Jiang+16 more|arXiv (Cornell University)|Aug 8, 2018

Superconducting Materials and Applications被引用 4

一句话总结

该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跑道线圈在无淬火情况下的稳定运行，实现了在3.5 T磁场下8.6 kA的电流和在4.2 K下1020 A/mm²的线材电流密度，且淬火行为可预测，局限于超过1米的高场区域，从而实现了可靠的保护机制，并开启了一种新型可预测淬火的高温超导磁体新范式。

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

• 开发基于高温超导体（HTS）的高场超导磁体，以克服Nb-Ti和Nb3Sn在临界电流密度和淬火稳定性方面的局限性。
• 通过实现长长度导体中稳定可靠的表现，解决传统HTS磁体中不可预测的淬火行为和长训练周期的挑战。
• 证明Bi-2212 Rutherford电缆可在无训练淬火的情况下实现高电流密度和稳定运行，从而推动实用化高场磁体应用。
• 建立一种基于Bi-2212的新磁体设计范式，具备可预测淬火、各向同性及千米级导线可扩展性。

提出的方法

• 采用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，以提升临界电流密度。
• 使用这些电缆绕制跑道线圈，并在4.2 K下逐步增加电流至8.6 kA，以评估性能和淬火行为。
• 测得峰值磁场为3.5 T，线材电流密度达1020 A/mm²，且在30 T下临界电流密度达到950 A/mm²。
• 通过空间分辨温度传感器监测淬火特性，以识别淬火起始和传播行为。
• 通过分析从磁通流到热失控的转变过程，评估热稳定性，重点关注一致性和可预测性。
• 将淬火行为与传统Nb-Ti、Nb3Sn和REBCO磁体进行比较，突出其在淬火位置和可预测性方面的差异。

实验结果

研究问题

• RQ1 Bi-2212 Rutherford电缆是否能在高电流密度和高场条件下实现稳定、无训练淬火的运行？
• RQ2 Bi-2212磁体中的淬火发生在何处？与其它HTS材料相比，其位置是否可预测？
• RQ3 在长长度Bi-2212多芯线材中，用于Rutherford电缆的线材电流密度最大可达到多少？
• RQ4 与Nb-Ti、Nb3Sn和REBCO磁体相比，Bi-2212磁体的淬火行为在空间定位性和热失控特性上有何不同？
• RQ5 Bi-2212线材的各向同性、圆形多芯结构是否能实现无需长时间训练周期的可扩展、可靠高场磁体构建？

主要发现

• Bi-2212跑道线圈在4.2 K下实现了8.6 kA的峰值电流，产生3.5 T的磁场，线材电流密度达1020 A/mm²。
• 整根线材的临界电流密度在30 T和4.2 K下达到创纪录的950 A/mm²，证明了长长度多芯线材的高性能表现。
• 在升流过程中未观察到训练淬火，表明其运行稳定可靠，且无需Nb-Ti和Nb3Sn磁体常见的长时间训练周期。
• 淬火始终在导体长度超过一米的高场区域起始，实现了可预测的淬火检测与保护。
• 淬火行为稳定且可预测，热失控在大范围内均匀发生，而非局限于局部薄弱点。
• 与Nb基超导体相比，Bi-2212磁体对能量扰动表现出更优的耐受性，从而开启了一种可预测淬火、可扩展的高场磁体新范式。