A simple screening current-induced magnetic field estimation method for REBCO pancake coils

The development of NMR/MRI REBa2Cu3Oy (REBCO, REBCO, RE =rare earth) magnets is happening all over the world. It has been found that screening current-induced magnetic fields (SCMFs) are a serious problem for NMR/MRI magnets wound with REBCO tapes. The reduction of SCMFs is strongly desired, and the estimation of SCMFs is also desired at the design stage of REBCO magnets. In order to evaluate a SCMF, a finite element method (FEM) or a boundary integration method is needed thus far, and a high-level simulation technique is required. In this paper, we develop an easy method to estimate a SCMF without a high-level simulation technique. In this method, the inductance of a winding turn is calculated and then a screening current is estimated according to the magnetic field penetrating into the winding turn. The SCMF is obtained from the estimated screening current. The SCMFs computed by the proposed method were compared with measurements and simulation results of the FEM. The results agreed well, but we can see a large difference. However, the SCMFs found by the proposed method are accurate enough to know they are at the design stage without the use of a high-level simulation technique.目前全球范围内均在推进核磁共振/磁共振成像（NMR/MRI）用稀土钡铜氧（REBa₂Cu₃O_y，REBCO，其中RE代表稀土元素）磁体的研发工作。研究表明，屏蔽电流感应磁场（screening current-induced magnetic fields，SCMFs）是采用REBCO带材绕制的NMR/MRI磁体所面临的严峻难题。亟需抑制SCMFs的负面影响，同时在REBCO磁体的设计阶段完成对SCMFs的预估。迄今为止，评估SCMFs需借助有限元法（FEM）或边界积分法，且需掌握高阶仿真技术。为此，本文提出一种无需高阶仿真技术即可预估SCMFs的简易方法。该方法先计算绕组匝的电感，再根据穿透绕组匝的磁场估算屏蔽电流，最终由估算得到的屏蔽电流计算得到SCMFs。将本文所提方法计算得到的SCMFs，与实测数据及FEM的仿真结果进行对比。尽管整体吻合度较好，但仍存在一定的显著偏差。不过，该方法所得的SCMFs预估精度已足以满足设计阶段的评估需求，无需依赖高阶仿真技术即可完成相关预估工作。