NMR spectrometers are considered to be an indispensable tool for structural biology. They are applied to determine the stereoscopic structure of protein molecules and to identify the chemical-reacting part between proteins and candidate medicines. Because the sensitivity and resolution of NMR spectrometers are improved with external magnetic fields, development projects of high-field NMR spectrometers have been carried out worldwide. At the Tsukuba Magnet Laboratory of the National Institute for Materials Science, the development of a high-field NMR magnet has been under way since 1995. The final target is to generate an additional 2.4T with an innermost coil, resulting in a central field of 23.5T corresponding to a 1H NMR frequency of 1GHz in a 54mm diameter room-temperature bore. The magnet was confirmed to operate as a high-resolution NMR magnet at 920MHz, using a Nb3Sn innermost coil. In the case of an NMR magnet, the required conditions of field homogeneity and stability are very strict. In this paper, we introduce the design issues of an NMR magnet by using our developed NMR magnet as an example. The future vision for high-field superconducting NMR magnets generating a field of 23.5T or more is also described.
