Japanese researchers succeeded in developing a 1.02GHz NMR (24T) in 2014. The next field target is a 1.3GHz (30.5T) and we have commenced designing a high resolution 1.3GHz LTS/HTS NMR magnet, operated in persistent current (PC) mode. The basic concept and relevant technical problems are identified in this paper.
To reduce the magnet size, high current density HTS coils are used that generate as high as 23T, enabling a compact magnet as small as a 800-900MHz LTS NMR magnet. Two probable designs have been examined so far; one uses reinforced-Bi2223 coils and the other REBCO/reinforced-Bi2223 coils. From a viewpoint of screening current, the former is better; while from a viewpoint of PC mode operation, the latter is preferred. The stress criteria are 350MPa in hoop stress and 50MPa in axial compressive stress; they are below the tolerance limit of the conductor. Numerical simulations of the screening current induced field are being developed; the magnet design will be modified later based on the simulation results. The RT bore may be enlarged to install stronger RT shims and ferromagnetic shims. The magnet will be self-shielded by a shielding coil for being installed in the NMR facility of RIKEN. 4K pulse tube cryocoolers will be installed to reduce helium consumption. We recently succeeded in developing a new type of superconducting joint between REBCO conductors, which may be available for use on this magnet. However, more investigations must be made in this regard. More details will be presented at the conference.
This work is supported in part by the MEXT. The authors would like to thank members of the HTS Magnet Technology Working Group in a program of the MEXT for their technical comments on the designs. Part of experimental data to be presented was obtained in the S-innovation Program of the JST.