Conceptual Design Proposal for the 40 T All-Superconducting Magnet

这项活动是国家强磁场实验室(NHMFL)40T超导(Sc)磁体项目的第二年。它描述了高温超导(HTS)测试磁体和必要的相关工作，以验证足以完成40T超导磁体概念设计的技术进步。在2013年国家研究委员会关于美国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。这一40T超导磁体将使美国能够通过另一次重大的“超导飞跃”，进一步决定性地提升其在SC磁体方面的领先地位，在数量上甚至超过其最近在全超导磁体中取得的32T的成就。投产后，40T SC磁体将成为NHMFL服务于其不断增长的用户群体的高场磁体套件中的旗舰产品。目前，NHMFL每年为2,000名用户提供11,000天的磁力时间，其中包括约700名博士生和约300名博士后，用于强磁场实验。这项研究从2012年到2018年在科学文献中产生了3180篇被引用的论文。新的磁铁将使用户获得超过36T的直流磁场的能力大约增加一倍。40T SC磁铁将在NHMFL的教育和公共外展项目中发挥重要作用，该项目每年通过课堂外展和实验室参观与10,000名K-12学生互动，以及10,000名各个年龄段的参观者参加NHMFL的年度开放参观。这一40T SC磁体的实现所带来的技术发展将为高场磁体在高能物理、聚变、X射线和中子设施、核磁共振和磁共振成像装置方面的前沿能力建立一个基准。40T SC磁体将使用类似于NHMFL目前世界纪录的32T Sc磁体的REBCO(稀土氧化钡铜氧化物)带状导体来建造。然而，40T SC磁体的特点是高温超导线圈的存储能量将增加约十倍，这将优先发展主动失超保护和减少线圈体积。因此，正在寻求两种替代导体技术：1)绝缘REBCO(I-REBCO)，它利用了对从32 T SC磁体项目中获得的失超行为的相对更好的了解；和2)无绝缘REBCO(NI-REBCO)，它显示出实现更高电流密度和显著紧凑线圈体积的潜力，NHMFL 2017年对长50 mm、直径34 mm的线圈进行了测试，在31T的背景磁场(由NHMFL阻性磁铁产生)中产生了45.5T的总场记录。在循环载荷和淬火期间可靠运行是这两种替代方案的核心开发目标。NHMFL在量化REBCO线圈中的屏蔽电流引起的应变方面取得了关键的见解，这为确保足够的疲劳寿命开辟了道路。先进的失超保护I-REBCO技术正在利用商业超导体和超级电容器的最新改进，在更高的电流密度下运行。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能被用于未来的60T混合磁铁。建成后，40T SC磁铁将为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。在实验能力方面的进展将包括四极核磁共振、比热和多门调谐光谱仪，以及系统的高压测量和通过重复样品剥离进行的系统维度交叉研究。这些量子物质的前沿包括高温超导、伊辛超导、重入超导、激子凝聚、非阿贝尔准粒子、各种形式的拓扑物质，以及作为经典多体量子相变的莫特相变的奥秘。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.