Conceptual Design Proposal for the 40 T All-Superconducting Magnet

该活动是国家高磁场实验室（NHMFL）40 T超导（SC）磁体项目的第二年。它描述了高温超导（HTS）测试磁体和相关工作，以验证技术进步足以完成40 T SC磁体的概念设计。在2013年美国国家研究理事会关于高磁场科学及其应用的报告中，40 T SC磁体和随后的60 T混合磁体都被列为国家优先事项。这种40 T超导磁体将使美国能够通过另一次伟大的“超导飞跃”进一步决定性地推进其在超导磁体领域的领导地位，甚至超过其最近在全超导磁体领域取得的32 T成就。在其调试后，40 T SC磁铁将成为NHMFL高场磁铁套件中的旗舰产品，为不断增长的用户社区服务。NHMFL目前每年为2，000名用户提供11，000天的磁体时间，其中包括约700名博士。学生和~300名博士后，用于高磁场实验。这项研究在2012年至2018年的科学文献中产生了3，180篇参考论文。新磁体将使用户对超过36 T的直流磁场的访问增加一倍。40 T SC磁体将在NHMFL的教育和公共宣传计划中发挥重要作用，该计划每年通过课堂宣传和实验室图尔斯参观与10，000名K-12学生互动，并吸引10，000名各年龄段的游客参加NHMFL的年度开放日。这种40 T SC磁体的实现所带来的技术发展将为与高能物理、聚变、X射线和中子设施、核磁共振、和磁共振成像装置。40 T SC磁体将使用REBCO（稀土钡铜氧化物）磁带导体类似于用于NHMFL的目前世界纪录的32 T SC磁铁。然而，40 T SC磁铁将使HTS线圈的储存能量增加约10倍，这优先考虑开发主动失超保护和减少线圈体积。因此，两种替代导体技术被追求：1）绝缘REBCO（I-REBCO），其利用从32 T SC磁体项目获得的对失超行为的相对更好的理解;和2）无绝缘REBCO（NI-REBCO），NHMFL 2017年对50 mm长的线圈进行的测试表明，该产品具有获得更高电流密度和线圈体积急剧压缩的潜力，直径为34 mm，在31 T背景磁场（由NHMFL电阻磁铁产生）中产生45.5 T总磁场的记录。在循环负载下和淬火期间的可靠运行是这两种替代方案的核心发展目标。NHMFL开发了关于量化REBCO线圈中屏蔽电流引起的应变的关键见解，这开辟了确保足够疲劳寿命的途径。通过利用商用超导体和超级电容器的最新改进，在更高电流密度下运行的先进失超保护I-REBCO技术正在进行中。NI-REBCO技术的发展重点是控制接触电阻和主动失超保护。这些发展中的任何一个都可以在未来的60 T混合磁体中使用。完成后，40 T SC磁体将为一次持续数天的实验提供非常低的噪声环境，超过目前的动力（电阻和混合）磁体。 实验能力的进步将包括四极核磁共振、比热和多门调谐光谱，以及通过重复样品剥离进行的系统高压测量和系统维度交叉研究。量子物质的这些前沿包括高温超导性、伊辛超导性、再入超导性、激子凝聚、非阿贝尔准粒子、无数形式的拓扑物质，和围绕莫特转变的谜团，该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准。

This activity is the second year of the 40T Superconducting (SC) Magnet project at the National High Magnetic Field Laboratory (NHMFL). It describes high-temperature superconducting (HTS) test magnets and related work necessary to validate technology advances sufficient to complete the conceptual design of a 40T SC magnet. Both a 40T SC magnet and a subsequent 60T Hybrid magnet were listed as national priorities in the 2013 National Research Council report on High Magnetic Field Science and Its Application in the United States. This 40T SC magnet will enable the United States to further and decisively advance its leadership in SC magnets via another great “superconducting leap”, exceeding in magnitude even its recent achievement of 32T in an all-superconducting magnet. Upon its commissioning, the 40T SC magnet will become a flagship in the NHMFL’s suite of high-field magnets that serve its growing user community. The NHMFL presently provides 11,000 days of magnet time annually to 2,000 users, including ~700 Ph.D. students and ~300 postdocs, for high-magnetic-field experiments. This research has resulted in 3,180 refereed papers in the scientific literature from 2012 to 2018. The new magnet will roughly double user access to DC magnetic fields exceeding 36T. The 40T SC magnet will be highly featured in the NHMFL’s education and public outreach programs that interact annually with 10,000 K-12 students via classroom outreach and lab tours and 10,000 visitors of all ages to the NHMFL’s annual Open House. The technology development resulting from the realization of this 40T SC magnet will set a benchmark for high-field magnets connected with frontier capabilities in high energy physics, fusion, X-ray and neutron facilities, nuclear magnetic resonance, and magnetic resonance imaging installations.The 40T SC magnet will be constructed using REBCO (Rare Earth Barium Copper Oxide) tape conductor similar to that used for the NHMFL’s present world-record 32T SC magnet. However, the 40T SC magnet will feature an approximately ten-fold increase in the stored energy of the HTS coils, which places priority on developing active quench protection and reducing coil volume. Two alternative conductor technologies are thus being pursued: 1) Insulated REBCO (I-REBCO), which exploits comparatively a much better understanding of quench behavior gained from the 32 T SC magnet project; and 2) No-Insulation REBCO (NI-REBCO), which shows potential to attain higher current density and dramatic compaction of coil volume as demonstrated by the NHMFL’s 2017 test of a coil 50mm long and 34mm in diameter that generated a record of a total field of 45.5T in a 31T background magnetic field (generated by an NHMFL resistive magnet). Reliable operation under cyclic loading and during quench are core development goals for both alternatives. The NHMFL developed key insights on quantifying strain due to screening currents in REBCO coils, which opens paths to ensure sufficient fatigue life. Advanced quench protection I-REBCO technology operating at higher current density is underway by exploiting recent improvement in commercial superconductors and super-capacitors. Development in NI-REBCO technology focuses on controlling contact resistance and active quench protection. Either of these developments may be employed in a future 60T hybrid magnet. When complete, the 40T SC magnet will provide a very low noise environment for experiments lasting days at a time, surpassing present-day powered (resistive and hybrid) magnets. Advances in experimental capabilities will include quadrupolar nuclear magnetic resonance, specific heat, and multi-gate tuning spectroscopies, as well as systematic high pressure measurements and systematic dimensionality crossover studies by repeated sample exfoliation. These frontiers in quantum matter include high temperature superconductivity, Ising superconductivity, re-entrant superconductivity, exciton condensation, non-Abelian quasiparticles, topological matter in its myriad forms, and the mysteries surrounding the Mott transition as the canonical many-body quantum phase transition.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.