Persistent-mode, Liquid-helium-free, Robust Bi2212 Magnets for MRI and >1GHz NMR

超导磁体是MRI系统所需要的，其可以在升高的温度下操作，并且 更高的磁场没有昂贵的，在许多地方，不可用的液氦是所需的低 温度超导体（LTS），并使NMR仪器能够在23 T LTS磁场极限以上运行。 高温超导体（HTS）为提高这些材料的性能提供了最佳选择。 仪器在较低成本的高温机械制冷，只要他们可以与 所需的形状、强度、均匀性和电流密度。磁铁技术部 (MTD)麻省理工学院弗朗西斯苦磁实验室（FBML）的研究人员，我们在第一阶段STTR计划中的合作伙伴，首先 1999年，我认识到并向NIH提出，基于HTS的导体必须被纳入MRI和NMR中 为了超越这些限制，我们需要使用磁铁。在高温超导导体中，只有2212线可以在很大程度上提供上级Je 更高的操作温度和磁场，同时原则上能够实现线形式，例如，圆形， 矩形，已被证明适用于LTS。然而，为了满足这一需求，必须开发2212线圈 具有：1）在长长度上改进的线应力和弯曲公差，以允许更简单的线圈制造和操作 具有大的洛伦兹力，2）超导接头的能力，以允许更低的成本和更均匀的场 通过持续电流操作模式，以及3）层绕结构中的高、均匀电流密度。固体 材料解决方案公司（SMS）目前正在开发强有力的矩形2212线材的线圈形式，重点是该计划 在第一个同类，持久模式HTS线圈，是由强大的2212线和超导接头。 首先，SMS与其合作伙伴MIT-FBML的MTD将开发一种超导联合技术， 强、矩形、高电流密度2212线。接头配置、熔体结构参数和焊丝/接头Ic 将根据一项初步研究的结果进行调查，该研究已经证明， 可以在2212导线端部之间产生接头。 其次，该技术将被应用于开发超导接头和原型持续电流 开关.将在加强线端之间制备接头，并完成热处理，然后进行 接头以及线圈部分。使用最佳样本，切换到持久模式的方法如下 建立与加热器，并与场衰减率的特点，以证明持续的电流承载关节 可以用盘绕的强2212线实现。 第三，第一个持久模式示范高温超导线圈将设计，生产和测试，基于我们的 强大的2212电线和线圈制造技术。这个线圈将被设计和建造，使它能够产生一个中心场 在Ic或低于Ic时高达约5 T，具有闭环超导接头，以及允许切换到持续的加热器 模式它将在4.2 K下以高达Ic的驱动电流模式进行测试，然后使用背景场进行测试，总场> 8 T.然后，它将被充电到不同的电流水平，然后切换到持久模式。测试将完成 测量其在高达约4 T的背景场中的场衰减率，以表征持续模式 性能和证明我们的能力，生产和经营基于强力丝2212线圈在持久模式。 当充分发展，这一进展将使实际生产的持久模式高温超导磁体的基础上，我们的 2212超导体，用于液体无氦，和更高场MRI以及>1GHz NMR系统。

Superconducting magnets are required for MRI systems that can operate at elevated temperatures and with higher magnetic field without the expensive and in many places, unavailable liquid helium that is required with Low Temperature Superconductors (LTS), and for enabling NMR instruments to operate above the 23 T LTS field limit. High Temperature Superconductors (HTS) provide the best options for advancing the performance of these instruments at the lower-cost elevated temperatures of mechanical refrigeration provided they can be made with the required form, strength, uniformity and current density into persistent current coils. The Magnet Technology Division (MTD) of the MIT Francis Bitter Magnet Laboratory (FBML), our partner in this Phase I STTR Program, was first to recognize and propose to the NIH in 1999, that HTS-based conductors must be incorporated into MRI and NMR magnets in order to surpass these limits. Among HTS conductors, only 2212 wire can provide superior Je in much higher operating temperatures and magnetic fields while in principle enabling wire forms, for example, round and rectangular, that are proven to work with LTS. However, in order to meet this demand, 2212 coils must be developed with: 1) improved wire stress and bend tolerance in long lengths to allow for simpler coil fabrication and operation with large Lorentz forces, 2) capability for superconducting joints to allow much lower costs and more uniform fields via persistent current operation modes, and 3) high, uniform current densities in layer-wound configurations. Solid Material Solutions (SMS) is now developing coiled forms of strong, rectangular 2212 wire with focus in this program on a first-of-its-kind, persistent mode HTS coil that is made with strong 2212 wire and superconducting joints. Firstly, SMS, with its partner, the MTD at MIT-FBML, will develop a superconducting joint technique for its strong, rectangular, high current density 2212 wire. Joint configuration, melt texture parameters and wire / joint Ic’s will be investigated based on the results of a preliminary study that has already demonstrated that a superconducting joint can be produced between 2212 wire ends. Secondly, the technique will be applied to develop superconducting joints and a prototype persistent current switch. Joints will be prepared between reinforced wire ends and heat treatments completed, followed by Ic tests of joints as well as coiled wire sections. Using the best samples, a method for switching to persistent mode will be established with heaters, and with field-decay rates characterized to demonstrate that persistent current carrying joints can be achieved with coiled strong 2212 wire. Thirdly, a first persistent mode demonstration HTS coil will be designed, produced and tested, based on our strong 2212 wire and coil making know-how. This coil will be designed and built so that it can generate a central field of up to about 5 T at or below Ic, with loop-closing superconducting joints, and heater to allow switching to persistent mode. It will be tested at 4.2 K in driven current mode up to Ic and then with a background field for a total field of > 8 T. It will then be charged to different current levels, followed by switching to persistent mode. Tests will be completed to measure its field decay rates in background fields up to about 4 T, in order to characterize persistent mode properties and demonstrate our capability to produce and operate strong-wire based 2212 coils in persistent mode. When fully developed, this advance will enable the practical production of persistent mode HTS magnets based on our 2212 superconductor, for use in liquid He-free, and higher field MRI as well as >1GHz NMR systems.