Accelerators magnets must have minimal magnetic field imperfections to reduce particle-beam instabilities. In the case of coils made of high-temperature superconducting (HTS) tapes, the magnetization due to persistent currents adds an undesired field contribution, potentially degrading the magnetic field quality. In this paper we study the use of superconducting screens based on HTS tapes for reducing the magnetic field imperfections in accelerator magnets. The screens exploit the magnetization by persistent currents to cancel out the magnetic field error. The screens are aligned with the main field component, such that only the undesired field components are compensated. The screens are self-regulating, and do not require any externally applied source of energy. Measurements in liquid nitrogen at show for dipole-field configurations a significant reduction of the magnetic field error up to a factor of four. The residual error is explained via numerical simulations accounting for the geometric defects in the HTS screens, achieving satisfactory agreement with experimental results. Simulations show that if screens are increased in width and thickness, and operated at , field errors may be eliminated almost entirely for the typical excitation cycles of accelerator magnets.

加速器磁铁必须具有最小的磁场缺陷，以减少粒子束的不稳定性。对于由高温超导 (HTS) 带制成的线圈，持续电流引起的磁化增加了不希望的磁场贡献，可能会降低磁场质量。在本文中，我们研究了使用基于 HTS 带的超导屏幕来减少加速器磁铁中的磁场缺陷。屏幕利用持续电流的磁化来抵消磁场误差。屏幕与主场分量对齐，以便仅补偿不需要的场分量。屏幕是自我调节的，不需要任何外部施加的能源。在液氮中的测量显示对于偶极场配置，磁场误差显着降低了四倍。残余误差通过数值模拟解释了 HTS 屏幕中的几何缺陷，与实验结果取得了令人满意的一致性。模拟表明，如果屏幕的宽度和厚度增加，并在 下运行，对于加速器磁铁的典型励磁循环，场误差几乎可以完全消除。