Hiroto Suematsu

Achievement of 1020 MHz NMR

We have successfully developed a 1020MHz (24.0T) NMR magnet, establishing the worlds highest magnetic field in high resolution NMR superconducting magnets. The magnet is a series connection of LTS (low-Tc superconductors NbTi and Nb3Sn) outer coils and an HTS (high-Tc superconductor, Bi-2223) innermost coil, being operated at superfluid liquid helium temperature such as around 1.8K and in a driven-mode by an external DC power supply. The drift of the magnetic field was initially ±0.8ppm/10h without the (2)H lock operation; it was then stabilized to be less than 1ppb/10h by using an NMR internal lock operation. The full-width at half maximum of a (1)H spectrum taken for 1% CHCl3 in acetone-d6 was as low as 0.7Hz (0.7ppb), which was sufficient for solution NMR. On the contrary, the temporal field stability under the external lock operation for solid-state NMR was 170ppb/10h, sufficient for NMR measurements for quadrupolar nuclei such as (17)O; a (17)O NMR measurement for labeled tri-peptide clearly demonstrated the effect of high magnetic field on solid-state NMR spectra.

Generation of 24 T at 4.2 K using a layer-wound GdBCO insert coil with Nb3Sn and Nb–Ti external magnetic field coils

High-temperature superconducting (HTS) magnets are believed to be a practical option in the development of high field nuclear magnetic resonance (NMR) systems. The development of a 600 MHz NMR system that uses an HTS magnet and a probe with an HTS radio frequency coil is underway. The HTS NMR magnet is expected to reduce the volume occupied by the magnet and to encourage users to install higher field NMR systems. The tolerance to high tensile stress is expected for HTS conductors in order to reduce the magnet in volume. A layer-wound Gd–Ba–Cu–O (GdBCO) insert coil was fabricated in order to investigate its properties under a high electromagnetic force in a high magnetic field. The GdBCO insert coil was successfully operated at a current of up to 321 A and an electromagnetic force BJR of 408 MPa in an external magnetic field generated by Nb3Sn and Nb–Ti low-temperature superconducting coils. The GdBCO insert coil also managed to generate a magnetic field of 6.8 T at the center of the coil in an external magnetic field of 17.2 T. The superconducting magnet consisting of GdBCO, Nb3Sn and Nb–Ti coils successfully generated a magnetic field of 24.0 T at 4.2 K, which represents a new record for a superconducting magnet.

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

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)Ba2Cu3O7-x (REBCO, RE: rare earth) conductors have an advantage over Bi2Sr2Ca2Cu3O10-x (Bi-2223) and Bi2Sr2CaCu2O8-x (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 worlds 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.

1020 MHz single-channel proton fast magic angle spinning solid-state NMR spectroscopy

This study reports a first successful demonstration of a single channel proton 3D and 2D high-throughput ultrafast magic angle spinning (MAS) solid-state NMR techniques in an ultra-high magnetic field (1020MHz) NMR spectrometer comprised of HTS/LTS magnet. High spectral resolution is well demonstrated.

REBCO Layer-Wound Coil Tests Under Electromagnetic Forces in an External Magnetic Field of up to 17.2 T

A nuclear magnetic resonance (NMR) system using a high-temperature superconducting (HTS) magnet and a probe with an HTS radio frequency coil is currently under development. The HTS NMR magnet is expected to reduce the volume occupied by the magnet and to encourage users to install higher field NMR systems. RE-Ba-Cu-O-coated (REBCO-coated) conductors offer the advantages of a higher critical current density than low-temperature superconductors in magnetic fields above 10 T as well as tolerance to high tensile stress. Both of these factors are expected to lead to a reduction in the volume of the magnet. Four REBCO layer-wound test coils were fabricated in order to investigate their properties under electromagnetic forces in an external magnetic field of up to 17. 2 T. The REBCO coils with a practical inner diameter were successfully operated under electromagnetic forces of over 200 MPa in high magnetic fields.

Present status of 920 MHz high-resolution NMR spectrometers

The first 920 MHz high-resolution NMR (nuclear magnetic resonance) magnet was successfully installed at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. A persistent operation at 21.6 T has continued since April 2002 without any problems. Excellent field stability of 0.31 Hz/h was observed from December 2002 to January 2003. Since July 2002, the magnet was used as an essential part of the only 920 MHz high-resolution NMR spectrometer in the world. The signal-to-noise ratio of 0.1% ethylbenzene using a proton-selective probe was as high as 2981. An HCN triple-resonance probe is now attached to the spectrometer to contribute to the National Project on Protein Structural and Functional Analysis in Japan. The completion of the second 920 MHz-class NMR spectrometer is scheduled for spring 2004.

Combination of high hoop stress tolerance and a small screening current-induced field for an advanced Bi-2223 conductor coil at 4.2 K in an external field

An advanced Bi-2223 conductor with Ni–Cr reinforcement is a likely candidate to achieve a compact super-high field nuclear magnetic resonance (NMR) magnet capable of operation beyond 1 GHz (23.5 T). However, the conductors must show both high hoop stress tolerance, typically >300 MPa, and a small screening current-induced magnetic field, both of which are essential for a compact magnet generating a highly accurate field. These two conditions have not yet been demonstrated in a working coil. This is the first paper to systematically investigate both characteristics for a layer-wound coil made with the advanced Bi-2223 conductor operated mainly at 4.2 K in an external field of ≤17 T. The coil tolerated a hoop stress of 370 MPa, even though the conductor had a bending strain corresponding to a diameter of 120 mm. On the other hand, the coil showed a notable screening current-induced field in a low external field, which may be explained by weak-link and direct contacts between highly packed Bi-2223 filaments in the silver matrix. The field sharply decreased with increasing external field between 0–1 T. Thus, the conductor should be useful for inner coils in compact super-high field NMR magnets.

Shimming for the 1020 MHz LTS/Bi-2223 NMR Magnet

Using a Bi-2223 innermost coil, the worlds first NMR magnet with a frequency beyond 1 GHz has been developed and operated at the National Institute for Materials Science during 2014-2015. The existing 920 MHz (21.6 T) NMR magnet was successfully upgraded to a 1030 MHz (24.2 T) magnet by replacing the Nb3Sn innermost coil with a Bi-2223 coil. After charging the magnet to 1020 MHz (24.0 T), a shimming operation was started to obtain the homogeneous magnetic field required for NMR measurements. However, a large magnetic field inhomogeneity appeared, which could not be compensated using conventional shimming methods, i.e., superconducting and room temperature shim coils. Therefore, a new ferromagnetic shimming technology was applied, which achieved powerful and fast-acting field compensation and performed comparably to active shimming. This enabled effective compensation of the magnetic field inhomogeneity, leading to a subsequently excellent NMR resolution test result of 0.7 ppb. This NMR resolution enables NMR measurements for a membrane protein sample.

Advanced field shimming technology to reduce the influence of a screening current in a REBCO coil for a high-resolution NMR magnet

This paper describes a field shimming technology to obtain a spatially homogeneous magnetic field required for a high-resolution nuclear magnetic resonance (NMR) magnet under the influence of a screening current in a (RE)Ba2Cu3O7–x (REBCO) coil. Use of REBCO inner coils is one solution to realize a super-high field (>23.5 T, 1 GHz) NMR magnet. However, a REBCO coil generates a large amount of field error harmonics due to the inhomogeneous coil winding introduced by a thin tape conductor. In addition, the performance of a field correction coil and outer superconducting (SC) shim coils are significantly reduced due to the shielding effect of the screening current in the REBCO coil. Therefore, conventional shimming technology using SC shim coils and room temperature shim coils cannot adequately compensate those field error harmonics and high-resolution NMR measurements are not possible. In the present paper, an advanced field shimming technology including an inner SC shim coil and a novel type of ferromagnetic shim were installed in a 400 MHz low-temperature SC/REBCO NMR magnet. The inner SC shim coil and the ferromagnetic shim compensated for the reduction in the performances of the field correction coil and the SC shim coils, respectively. The field error harmonics were greatly compensated with the technology and a high NMR resolution <0.01 ppm was obtained. The results from the present work suggest an optimal shimming procedure for a super-high field NMR magnet with high-temperature superconductors inner coils, i.e. the best mix of shims.

Degradation of a REBCO Coil Due to Cleavage and Peeling Originating From an Electromagnetic Force

This paper presents the results of a high field generation test for layer-wound HTS coils in a background magnetic field. The test revealed new types of degradation for a REBCO coil caused by an electromagnetic force. A series-connected REBCO coil and a Bi-2223 coil were charged at 4.2 K in a background magnetic field of 17.2 T to generate a central magnetic field of 28.2 T (nuclear-magnetic-resonace frequency of 1.2 GHz). However, a premature normal voltage appeared on the REBCO coil, and the charging was stopped at 25 T. Unwinding the REBCO coil after the experiment found: 1) delamination, due to a cleavage and peeling, of the conductor in a soldered joint inside the winding; and 2) axial movement and edgewise bend deformation of the REBCO conductor at the outermost layer. The keyword of the present degradation is stress concentration, which is also the origin of the more widely known thermal stress-induced degradation.