Prototype REBCO Z1 and Z2 shim coils for ultra high‑fieldhigh‑temperature superconducting NMR magnets

We present promising results of novel high‑temperature superconducting (HTS) shim coil prototypes that circumvent the size and strength limitation of our earlier innovative HTS shim concept based on 46‑mm wide REBCO tape. The HTS shim coil is placed inside the HTS magnet, mainly for ultrahigh‑field (> 1 GHz or 23.5 T) NMR magnets, and thus unaffected from the windings’ diamagnetic wall effects. One full‑scale version will be applied to clean up Z1 and Z2 harmonic errors in the MIT 1.3‑ GHz high‑resolution NMR magnet composed of an 835‑MHz HTS insert, while another version for an MIT 1‑GHz microcoil NMR magnet whose small‑scale model we are currently building. The prototype sets were wound with a 2‑pile, 1.03‑mm wide, 0.30‑mm thick REBCO conductor. Operated at 77 K, the Z1 shim set generated a 1st harmonic field strength of 179 kHz/cm at 70 A, while the Z2 shim set, composed of two pairs, Z21 and Z22, generated the 2nd harmonic field of 141 kHz/cm2 at 50 A. Together with discussion on technical challenges for this REBCO shim coil concept, we demonstrate its feasibility for the next generation of ultra‑high‑field (UHF) HTS NMR magnets.

本研究展示了新型高温超导（high-temperature superconducting, HTS）匀场线圈原型的极具前景的实验结果，该原型突破了本团队此前基于46毫米宽REBCO带材的创新性高温超导匀场方案所存在的尺寸与场强限制。该高温超导匀场线圈内嵌于高温超导磁体内部，主要应用于超高场（>1吉赫兹或23.5特斯拉）核磁共振（nuclear magnetic resonance, NMR）磁体，因此不受绕组抗磁壁效应的影响。一款全尺寸原型将用于校正麻省理工学院（MIT）1.3吉赫兹高分辨率NMR磁体中的Z1、Z2谐波误差，该磁体搭载835兆赫兹高温超导插入线圈；另一款原型则将应用于MIT 1吉赫兹微线圈NMR磁体，该磁体的小型模型目前正在搭建中。本次研制的原型线圈均采用2叠层、1.03毫米宽、0.30毫米厚的REBCO导体绕制而成。在77开尔文温度下运行时，Z1匀场组在70安培电流下可产生179千赫兹/厘米的一次谐波场强；而由Z21、Z22两对线圈组成的Z2匀场组，在50安培电流下可产生141千赫兹/平方厘米的二次谐波场。本文在讨论该REBCO匀场线圈方案所面临的技术挑战的同时，验证了其在下一代超高场（ultra-high-field, UHF）高温超导NMR磁体中的应用可行性。