Conceptual Design Proposal for the 40 T All-Superconducting Magnet

本次活动是国家强磁场实验室（NHMFL） 40T超导磁体项目的第二年。它描述了高温超导（HTS）测试磁体以及验证技术进步足以完成40T SC磁体概念设计所需的相关工作。在2013年美国国家研究委员会关于强磁场科学及其应用的报告中，40T SC磁体和随后的60T混合磁体都被列为国家优先事项。这种40T超导磁体将使美国通过另一次伟大的“超导飞跃”进一步和果断地推进其在超导磁体方面的领导地位，甚至超过其最近在全超导磁体方面取得的32T的成就。在调试后，40T SC磁铁将成为NHMFL高场磁铁套件的旗舰产品，为其不断增长的用户社区服务。NHMFL目前每年为2000名用户提供11,000天的磁体时间，其中包括约700名博士生和约300名博士后，用于高磁场实验。从2012年到2018年，这项研究在科学文献中发表了3180篇论文。新磁铁将使用户接触超过36T的直流磁场的机会增加一倍。40T SC磁铁将在NHMFL的教育和公共推广计划中发挥重要作用，该计划每年通过课堂推广和实验室参观与10,000名K-12学生互动，并在NHMFL的年度开放日接待10,000名各年龄段的游客。实现这种40T SC磁体所带来的技术发展将为高能物理、聚变、x射线和中子设施、核磁共振和磁共振成像装置等前沿能力相关的高场磁体设定基准。40T SC磁铁将使用REBCO（稀土钡铜氧化物）带导体构建，类似于用于NHMFL目前世界纪录的32T SC磁铁。然而，40T SC磁体将具有大约十倍的HTS线圈存储能量增加，优先考虑开发主动淬火保护和减少线圈体积。因此，正在研究两种替代导体技术：1)绝缘REBCO (I-REBCO)，它利用了从32 T SC磁体项目中获得的对淬火行为的更好理解；2)无绝缘REBCO (NI-REBCO)， NHMFL在2017年测试了一个长50mm、直径34mm的线圈，在31T的背景磁场（由NHMFL电阻磁体产生）中产生了45.5T的总磁场记录，证明了它具有更高的电流密度和线圈体积的显著压实性。在循环载荷下和淬火期间的可靠运行是这两种方案的核心发展目标。NHMFL在通过筛选REBCO线圈中的电流来量化应变方面取得了重要进展，为确保足够的疲劳寿命开辟了道路。利用商业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的淬火保护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淬火保护。这些发展中的任何一个都可能在未来的60T混合磁体中使用。完成后，40T SC磁铁将为一次持续数天的实验提供非常低的噪音环境，超过目前的动力（电阻和混合）磁铁。实验能力的进步将包括四极核磁共振、比热和多栅极调谐光谱，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。量子物质的前沿领域包括高温超导、伊辛超导、可重入超导、激子凝聚、非阿贝尔准粒子、无数形式的拓扑物质，以及围绕莫特跃迁（典型多体量子相变）的奥秘。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.