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

Abstract

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.