High resolution NMR measurements using a 400MHz NMR with an (RE)Ba2Cu3O7-x high-temperature superconducting inner coil: Towards a compact super-high-field NMR.

Use of high-temperature superconducting (HTS) inner coils in combination with conventional low-temperature superconducting (LTS) outer coils for an NMR magnet, i.e. a LTS/HTS NMR magnet, is a suitable option to realize a high-resolution NMR spectrometer with operating frequency >1GHz. From the standpoint of creating a compact magnet, (RE: Rare earth) Ba2Cu3O7-x (REBCO) HTS inner coils which can tolerate a strong hoop stress caused by a Lorentz force are preferred. However, in our previous work on a first-generation 400MHz LTS/REBCO NMR magnet, the NMR resolution and sensitivity were about ten times worse than that of a conventional LTS NMR magnet. The result was caused by a large field inhomogeneity in the REBCO coil itself and the shielding effect of a screening current induced in that coil. In the present paper, we describe the operation of a modified 400MHz LTS/REBCO NMR magnet with an advanced field compensation technology using a combination of novel ferromagnetic shimming and an appropriate procedure for NMR spectrum line shape optimization. We succeeded in obtaining a good NMR line shape and 2D NOESY spectrum for a lysozyme aqueous sample. We believe that this technology is indispensable for the realization of a compact super-high-field high-resolution NMR.