Portable, high magnetic field charging of bulk superconductors for practical engineering applications

当冷却到低温时，块状超导体可以用作产生几特斯拉磁场的超强、稳定的永久磁体，而传统永磁体的极限是1.5-2特斯拉，如钕磁铁(ND-Fe-B)。这使得它们对依赖高磁场的许多工程应用具有吸引力，包括具有前所未有的功率密度的紧凑型和高能效电机/发电机，以及紧凑型和便携式磁共振成像(MRI)和核磁共振(核磁共振)系统。现在，科学家还可以利用强磁场来利用材料的磁性来控制化学和物理过程，例如，这对磁分离和磁性药物输送系统(MDDS)很有吸引力。块体超导体磁体的主要优点是，可用的磁场可以比传统的永磁体高一个数量级(已经证明块体高温超导体能够捕获大于17特斯拉的磁场)，并且不需要电源和直接连接来提供产生磁场的电流，就像在电磁中一样。块体超导体的磁化过程基本上涉及施加和去除大磁场，该大磁场在材料中感应循环超导电流而不产生电阻。然而，目前面临的一个重大挑战是实现一种简单、可靠和便携的充电技术来磁化这类超导体，这对于为高场强、磁通型超导应用生产具有竞争力和紧凑性的设计至关重要。目前最著名的磁化块状超导体的方法实际上是脉冲场磁化(PFM)技术，即通过毫秒量级的脉冲施加大磁场。然而，使用PFM的世界纪录在29K时只有5.2特斯拉，远远低于这些材料的真实能力。PFM技术有许多设计考虑因素：脉冲的大小和持续时间(S)，施加脉冲的数量，磁化线圈/夹具的类型和形状，如何冷却块状超导体，以及施加脉冲的温度(S)。所有这些考虑因素都将通过数值模拟进行分析，以便针对便携式高场磁体系统彻底优化PFM设置。通过实验结果验证，数值模拟是解释实验结果和材料在磁化过程中的物理机制的一种特别重要和经济有效的方法。这样的建模工具还可以用来预测和提出新的磁化技术，这在实验上更难实现。这项研究计划的主要目标是为实际工程应用开发便携式、高磁场的块状超导体充电，最终目标是生产便携式和商业可行的高场磁体系统。这将得到以下方面的支持：为高场应用量身定做大块超导体和磁体几何形状的材料加工和性能，开发完整的电磁-热-机械分析的数值模型，以避免在涉及到强磁场时潜在的机械断裂(&gt；6-7特斯拉)，并进行实验以验证这些模型，以及开发考虑到上述所有设计考虑的优化的PFM技术。将围绕螺线管和分离式磁化线圈开发两种类型的脉冲充电系统，这些系统将用于在高于40K的温度下实现超过当前记录的5特斯拉的捕获场，并作为特定应用定制设计的概念验证。

Bulk superconductors can be used, when cooled to cryogenic temperatures, as super-strength, stable permanent magnets generating fields of several Tesla, compared to the 1.5-2 Tesla limit for conventional permanent magnets, such as neodymium magnets (Nd-Fe-B). This makes them attractive for a number of engineering applications that rely on high magnetic fields, including compact and energy-efficient motors/generators with unprecedented power densities and compact and portable magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) systems. It is now also possible for scientists to use high magnetic fields to exploit the magnetism of a material for controlling chemical and physical processes, which is attractive for magnetic separation and magnetic drug delivery systems (MDDS), for example. The chief advantage of a bulk superconductor magnet is that the available field can be up to an order of magnitude higher than conventional permanent magnets (bulk high-temperature superconductors have been shown to be capable of trapping magnetic fields greater than 17 Tesla) and no power supply and direct connection is necessary to supply the current producing the magnetic field, as in electromagnets.The magnetisation process of a bulk superconductor essentially involves the application and removal of a large magnetic field that induces a circulating supercurrent in the material that flows without resistance. However, one significantly challenging problem currently faced is achieving a simple, reliable and portable charging technique to magnetise such superconductors, and this is crucial to producing competitive and compact designs for high-field, trapped flux-type superconducting applications. The current, best-known method for magnetising bulk superconductors practically is the pulsed field magnetisation (PFM) technique, whereby a large magnetic field is applied via a pulse on the order of milliseconds. However, the world record using PFM is only 5.2 Tesla at 29 K, which is much less than the true capability of these materials. The PFM technique has many design considerations: the magnitude and duration of the pulse(s), the number of applied pulses, the type and shape of the magnetising coil/fixture, how the bulk superconductor is cooled, and the temperature(s) at which the pulse(s) are applied. All of these considerations will be analysed through numerical modelling in order to thoroughly optimise the PFM setup in view of a portable, high-field magnet system. Numerical modelling, validated by experimental results, is a particularly important and cost-effective method to interpret experimental results and the physical mechanisms of the material during the magnetisation process. Such modelling tools can also be used to predict and propose new magnetising techniques, which is more difficult to achieve experimentally. The primary objective of this research programme is to develop portable, high magnetic field charging of bulk superconductors for practical engineering applications, with an end goal of producing portable and commercially-viable high-field magnet systems. This will be underpinned by the tailoring the material processing and properties of bulk superconductors and magnet geometry for high field applications, developing numerical models for complete electromagnetic-thermal-mechanical analysis to avoid potential mechanical fracture when high magnetic fields are involved (> 6-7 Tesla) and carrying out experiments to validate such models, and the development of an optimised PFM technique that takes into account all of the design considerations above. Two types of pulsed charging systems will be developed around solenoid- and split-type magnetising coils, which will be used to achieve trapped fields in excess of 5 Tesla, the current record, at temperatures greater than 40 K and as a proof-of-concept for bespoke designs for specific applications.