R&D of High-Field NMR systems
・Development of a 920 MHz (21.6T) High-Resolution NMR Magnet
In 2001, a very high-field superconducting NMR magnet, developed by the former IMR (Institute for Materials Research), Kobe Steel, Ltd., JEOL Ltd., and others, was completed. This magnet enabled operation in persistent current mode at 21.6 T—the corresponding proton resonance frequency is 920 MHz. For the wire used in the innermost coil, which is exposed to the strongest magnetic field region, a bronze-process, Ti-doped Nb₃Sn wire with a tin concentration increased up to 15 wt.% in the bronze was used. The cooling system was also improved to allow more efficient operation at lower temperatures. In addition, partial field homogeneity was achieved by using a superconducting shim coil, which made it possible to reach the highest field of 21.64 T and transition to stable operation in the 920 MHz persistent current mode, all while maintaining excellent field stability, suppressed to 3 Hz/h—an essential factor for NMR magnets. This achievement represented a significant step towards the development of 1 GHz-class NMR magnets being carried out as part of the Ministry of Education, Culture, Sports, Science and Technology’s (MEXT) Superconducting Materials Research Multi-Core Project.
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Persistent-mode operation of a 920 MHz high-resolution NMR magnet
T. Kiyoshi et al., IEEE Trans. Appl. Superconductivity, 12(1), 2002, 711-714. -
Achievement of a 920-MHz high resolution NMR
K. Hashi et al., Journal of Magnetic Resonance, 156(2), 2002, 318-321.
・Development of a 930 MHz (21.9 T) High-Resolution NMR Magnet
In 2004, a research team led by NIMS developed a high-resolution NMR magnet operating at 21.9 T—the highest magnetic field in the world at the time, corresponding to a proton resonance frequency of 930 MHz. By using Ti-doped Nb₃Sn wire with a tin concentration of 16 wt.%, which exceeds that of the inner coil wire used in the 920 MHz magnet, the critical current density was improved, making it possible to conduct the same current with a smaller cross-sectional area. As a result, the 930 MHz (21.9 T) magnetic field was achieved using the same operating current as the 920 MHz magnet. The successful development of this state-of-the-art superconducting NMR magnet in Japan, ahead of the rest of the world, contributed significantly to advances in protein structure and function analysis, as well as in materials research such as solid-state catalysts, at a time when the importance of cutting-edge measurement and analytical technologies and equipment was rapidly increasing.
・Development of a 1,020 MHz (24.0 T) High-Resolution NMR Magnet
In 2015, a research team consisting of NIMS, RIKEN, Kobe Steel, Ltd., and JEOL RESONANCE Inc. (a consolidated subsidiary of JEOL Ltd.) succeeded in developing an ultra-high-field NMR device capable of generating the strongest magnetic field in the world at that time—24.0 T (corresponding to a resonance frequency for hydrogen of 1,020 MHz)—as part of the JST Advanced Measurement and Analysis Technology and Equipment Development Program "Development of 1 GHz-class NMR System." Furthermore, the team conducted actual measurements using this device and confirmed that both sensitivity and resolution were significantly improved compared to conventional NMR. Magnetic field strength is one of the key parameters in NMR devices, and there had been intense global competition to exceed 1,000 MHz (1 GHz). It had been long believed that exceeding 1,000 MHz would be possible using high-temperature superconducting technology; however, there were various difficulties, such as high-temperature superconductors being brittle and difficult to process, and it had not been achieved worldwide for many years. Through the development of several new technologies—including the fabrication of high-temperature superconductor (Bi-2223) wires originally developed at NIMS in 1988—the team achieved the world's highest field of 1,020 MHz with the NMR device.
It took 20 years from conception to achievement. The project overcame numerous obstacles, including an interruption just before completion due to damage from the Great East Japan Earthquake, a global helium supply crisis, and even the sudden passing of the team leader. After eight years of construction, the goal was finally accomplished.
