Genetic-Algorithm-Based Room-Temperature Shimming and Long-Term Operational Protocol for a KBSI 400 MHz all-HTS NMR Magnet

We report room-temperature (RT) shimming results and a long-term operational protocol for a Korea Basic Science Institute (KBSI) 400 MHz high-temperature superconducting (HTS) nuclear magnetic resonance (NMR) magnet composed of 48 all-REBCO double-pancake (DP) coils cooled by a cryo-cooler to be operated under 20 K. The spatial magnetic field homogeneity of the 400 MHz HTS NMR magnet improved from 0.95 ppm to 0.2 ppm due to the use of a genetic-algorithm-based RT shimming method, of which the feasibility had been verified beforehand through an earlier study of a low-temperature superconducting (LTS) NMR magnet. We also confirmed that the field homogeneity of the HTS NMR magnet varied slightly over time due to the screening-current-induced field (SCF) and the temporal instability of the magnet power supply during long-term operation. Because fluctuations in the field quality affect the pe…