Operation of a 400 MHz NMR magnet using a (RE:Rare Earth)Ba2Cu3O7− high-temperature superconducting coil: Towards an ultra-compact super-high field NMR spectrometer operated beyond 1 GHz

Abstract

High-temperature superconductors (HTS) are the key technology to achieve super-high magnetic field nuclear magnetic resonance (NMR) spectrometers with an operating frequency far beyond 1GHz (23.5T). (RE)BaCuO (REBCO, RE: rare earth) conductors have an advantage over BiSrCaCuO (Bi-2223) and BiSrCaCuO (Bi-2212) conductors in that they have very high tensile strengths and tolerate strong electromagnetic hoop stress, thereby having the potential to act as an ultra-compact super-high field NMR magnet. As a first step, we developed the world's first NMR magnet comprising an inner REBCO coil and outer low-temperature superconducting (LTS) coils. The magnet was successfully charged without degradation and mainly operated at 400MHz (9.39T). Technical problems for the NMR magnet due to screening current in the REBCO coil were clarified and solved as follows: (i) A remarkable temporal drift of the central magnetic field was suppressed by a current sweep reversal method utilizing ∼10% of the peak current. (ii) A Z2 field error harmonic of the main coil cannot be compensated by an outer correction coil and therefore an additional ferromagnetic shim was used. (iii) Large tesseral harmonics emerged that could not be corrected by cryoshim coils. Due to those harmonics, the resolution and sensitivity of NMR spectra are ten-fold lower than those for a conventional LTS NMR magnet. As a result, a HSQC spectrum could be achieved for a protein sample, while a NOESY spectrum could not be obtained. An ultra-compact 1.2GHz NMR magnet could be realized if we effectively take advantage of REBCO conductors, although this will require further research to suppress the effect of the screening current.

NMR of Macromolecular Assemblies and Machines at 1 GHz and Beyond: New Transformative Opportunities for Molecular Structural Biology

“…However, 1–1.1 GHz is believed to be the upper limit for magnets produced with only LTS materials due to limitations such as current density and temperature (1). Recent advancements have focused on the development of dual LTS/HTS (high temperature superconducting) magnets (1, 3, 10–13) wherein the inner HTS coil(s) are surrounded by outer LTS coil(s) (Figure 1). The development of HTS materials (14), such as Rare Earth BaCo oxides (REBCO, e.g.…”

Achievement of 1020 MHz NMR

“…The homogeneity of the magnetic field was sequentially adjusted by SC, ferromagnetic shims [16] and RT shims, based on the magnetic field data collected along a spiral locus. As some error components were extremely large, it was improbable to achieve sufficient magnetic field homogeneity without using ferromagnetic shims.…”

Engineering current density in excess of 200 A mm−2at 20 T in CORC®magnet cables containing RE-Ba2Cu3O7−δtapes with 38μm thick substrates

“…Figure 9 includes a fit to the data using a power-law function of equation 3, with p=0.72. Extrapolating the magnetic field dependence of I c using equation (3) would predict an I c at 20 T of 6130 A, or a J E at 20 T of 216.8 A mm −2 . The value of p=0.72 as determined from the cable measurement is slightly lower than the value of 0.76 measured on the single tapes.…”

“…Critical current as a function of magnetic field of three REBCO coated conductors measured at 4.2 K with the magnetic field applied perpendicular to the wide side of the tape. The straight solid lines are fits to the data on a full logarithmic scale according to equation(3).…”