Prototype REBCO Z1 and Z2 shim coils for ultra high-field high-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 ultra-high-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.

Completion of 25.2 T ultrahigh magnetic field NMR user facility in China

“…It is noted that such a homogeneous magnetic field distribution is unexpected for a DP magnet, demonstrating the validity of the DP order and precise notch optimization. We then applied Z1 and Z2 shim coils in the variable temperature cavity to further reduce the non-homogeneous harmonic components [24]. These shim coils were installed on an extension rod to reach the central measurement area.…”

Screening current induced magnetic field and stress in ultra-high-field magnets using REBCO coated conductors

“…Strong nonlinear behaviors including a reduction of the shimming strength were observed in LTS/Bi-2223 magnets [7,63] and LTS/REBCO magnets [25]. To improve the performance of the field shimming, additional shim strategies are needed, such as the shim coils located inside the HTS magnet [27,[64][65][66][67] and the passive ferromagnetic shim along with the room temperature shim [25,30].…”