考虑屏蔽电流影响的高温超导磁体高均匀度磁场生成问题的研究

The high temperature superconducting (HTS) magnet is an important part of the ultra-high field NMR superconducting magnet, however, there will be unstable and non-uniform screening current flowing in the HTS tapes when it is exposed to a perpendicular magnetic field, which will deteriorate the field homogeneity of HTS magnet. And also, the variations of the screening current induced by the temperature field changing and the large electromagnetic stress will also have an effect on the he homogeneity of the magnetic field. So, it is necessary to solve the major problems of generating high homogeneous magnetic field faced by the HTS magnet. Through the combination of theoretic and experimental methods, the main research contents of this project include: 1) Studying the effects of unstable and non-uniform screening current on the homogeneity of magnetic field; 2) Studying the design factors that have effects on the electromagnetic design of a HTS magnet with high homogeneous field with considering the effect of the screening current. 3) Studying the factors that affects the field distribution and homogeneity, e.g., temperature field distributions and strain distributions; 4) Studying the method of generating pulse heat flux through adding "heating plate" in the HTS magnet to eliminate the effect of screening current, and investigating the shimming systems suitable for the HTS magnet. Through the research work in this project, we want to reveal the laws of many factors how to affect the generation of high homogeneity field in the HTS magnet, and investigate the methods with high efficiency to increase the field homogeneity in the HTS magnet.

高温超导磁体是极高场超导核磁共振设备的重要组成部分，但是，由于高温超导带材受到磁场的作用会产生非稳态不均匀分布的屏蔽电流，恶化磁场的均匀性；同时磁体温度场变化导致的屏蔽电流改变和大电磁应力状态也会对磁场均匀性产生影响，导致高温超导磁体难以生成高均匀度的磁场。本项目将针对高温超导磁体中高均匀度磁场生成的问题，在前期研究的基础之上，拟采用理论和实验相结合的方法，展开以下研究：1. 研究非稳态不均匀分布屏蔽电流对高温超导线圈中磁场不均匀分量影响的规律；2. 探究在考虑屏蔽电流作用下影响高均匀度高温超导磁体电磁结构设计的主要因素和影响规律；3. 研究温度场、应力场对磁场分布及均匀度的影响规律；4. 研究采用磁体内置“加热片”产生脉冲热通量的方式消除屏蔽电流的方法，以及适用于高温超导磁体的匀场系统工作特性。通过研究，揭示高温超导磁体高均匀度磁场生成受多因素影响的规律，探索提升磁场均匀度的有效方法。

本项目针对高温超导磁体中非稳态不均匀分布屏蔽电流带来的工作区域磁场时间和空间不稳定性问题，开展REBCO高温超导磁体屏蔽电流分布特性及其消除方法的研究。针对高温超导磁体在复杂电磁环境下的实际运行工况，运用理论和实验方法，分别建立稳态和动态屏蔽电流分析模型，在充分考虑高温超导带材临界电流对磁场大小和角度依赖强不对称性的前期下，研究屏蔽电流的分布对于高温超导磁体磁场分布的影响；针对极高场无绝缘高温超导磁体，提出精细化网格电路计算模型，基于温度场和磁场对于临界电流的影响，研究充放电过程中高温超导磁体内不同位置带材中屏蔽电流随时间的动态变化过程；在理论分析和实验研究的基础之上，提出了热控消除屏蔽电流的方法，为传导冷却高温超导磁体的设计以及建造提供了重要的参考。该项目的研究成果对于高温超导磁体在电力设备、储能设备，生物医学工程设备，高精度科学仪器设备以及空间探测仪器等领域的应用具有重要的意义。