新型铁基超导线材电磁及机械特性提高研究

The recently discovered iron-based superconductors with very high upper critical field and small anisotropy have been regarded as a potential candidate material for high field applications. The critical current density of the iron-based superconducting tapes and wires has reached 10^5A/cm^2 at 4.2K, 10T, over the critical point for practical uses. However, there are still some problems before it can be used for practical application. One of the problems is that the mechanical strength of the pnictide wires cannot meet the requirement of coils running in high magnetic field. This project will investigated the influence of some parameters, such as temperature, stress, interface resistance, on the superconducting property of iron-based superconducting tapes and wires. Two kinds of methods, the composite sheath and the brazing, will be tried to improve the mechanical and electromagnetic properties of the pnictide wires. The effect of wire fabrication technique on the superconducting properties, such as tensile strength, flexural properties and electromagnetic characteristics, will be analyzed. Based on iron-based superconducting tapes and wires with the high strength, high electromagnetic properties, demonstration coil will be fabricated and tested. The data obtained in this project will provide basic information for the fabrication of high performance pnictide coils in future.

铁基超导体具有优异的高场特性，可望应用于NMR等高场磁体的内插线圈。目前铁基超导线带材的临界电流密度已经达到实用化水平，但其机械强度较低，远小于超导线圈在强磁场背景下运行时对其线材机械强度的要求。本课题拟通过分析温度、应力、界面电阻等参数对铁基超导线带材临界电流密度的影响规律，分别从复合包套和钎焊加强带两种工艺出发，探索提高铁基超导线带材机械性能和电磁特性的工艺参数。分析铁基超导线带材经过机械性能强化后超导性能变化的一般规律，并通过系统的机械性能和电磁性能实验研究对机械性能强化后的超导线带材的拉伸强度、弯曲特性、电磁特性等进行表征，从而对机械性能强化工艺进行验证和反馈。在获得具有高强度、高电磁特性的铁基超导线带材的基础上，通过小型铁基超导线圈的绕制及强磁场背景下的实验研究，获得铁基超导线带材在强磁场背景下的电磁特性，为制备实用化铁基超导线圈奠定坚实基础。

铁基超导体具有极高的临界磁场及各向异性小等独特优势，在下一代高场超导磁体，高能粒子加速器，核磁共振谱仪等领域极具应用潜力。本项目针对铁基超导线材在高场应用时面临的问题，开展了临界电流提高机制、机械性能提高途径及其对临界电流密度的影响、线材制备工艺优化、高场内插线圈研制及测试等。采用热压或热等静压工艺，调控铁基超导体的晶界状态，提高超导芯的致密度，改善晶粒之间的弱连接，制备出了高临界电流密度的铁基超导带材，最高临界电流密度在4.2K、10T达到1.5×10^5 A/cm^2，处于目前世界领先水平。通过对复合包套线材的加工技术进行了研究，通过优化包套材料和导体结构设计，获得了复合包套线材制备的基本参数，显著提高了铁基超导线材的机械性能。通过对机械加工工艺和热处理过程的系统优化，在国际上率先制备出了具有良好均匀性的100米级铁基超导线材，被誉为铁基超导材料实用化进程中的里程碑。使用研制的铁基超导长线，通过与合肥强磁场实验室合作研制了基于铁基超导材料的高场内插线圈，其中单饼线圈在30T下的临界电流达到62A，约为短样临界电流的72%，展示了铁基超导材料在高场下良好的应用特性。目前已发表高水平论文18篇(SCI收录，标注课题资助号)，申请国家发明专利5项。