930MHz NMRマグネットの開発

抄録

The first 920 MHz high-resolution NMR magnet has been operating at the Tsukuba Magnet Laboratory (TML) of the National Institute for Materials Science since April 2002. It has proved its effectiveness by determining the three-dimensional structures of protein molecules. To accelerate studies in structural biology and solid-state NMR, a second high-field NMR magnet was developed and installed at TML. Although its basic design was based on that of the 920 MHz NMR magnet, some parts have been improved. We applied a 16 wt.% Sn bronze-processed (Nb,Ti)₃Sn conductor for the innermost coil, replacing the 15 wt.% Sn conductor. This enabled a size reduction of 3.50 mm x 1.75 mm in the first magnet to 2.80 mm x 1.83 mm in the second because of an improvement of more than 20% in critical current density. As the magnetic field generated by the innermost coil was increased, at the same operating current of the first magnet, operation at 930 MHz was expected. The magnet was energized up to 21.6 T without any quenching and operated in a persistent mode at 920 MHz for more than one month. On March 24, 2004, it was excited up to 930 MHz. After the central field was increased to 21.89 T once, it was decreased to 21.86 T, and the persistent-mode operation started from a frequency of 930.7 MHz. This is the highest field that the magnets made of NbTi and Nb₃Sn coils have ever achieved. The field stability and the field homogeneity were measured and it was confirmed that this magnet can be applied as an NMR magnet.