45 Tesla Hybrid Magnet: Information for NMR/MRI Users

The 45 tesla hybrid magnet, access room at top flange.

The MagLab's 45 Tesla hybrid magnet is the highest continuous magnet field available in the world. The outer superconducting coil produces static field of about 11 Tesla, with the rest of the field being generated by water-cooled resistive insert. Bore size diameter is 32 mm. This magnet was not designed with NMR homogeneity in mind, and its field instability is not to NMR specs. Field stability in resistive magnets is compromised by fluctuations in power supply and in temperature of the cooling water.

Nevertheless, preliminary studies show great promise for using the highest magnet field available in the world for solid state NMR of quadrupolar nuclei especially for sites with very large quadrupolar couplings. These sites are too broad for observation at lower magnetic fields and are often called "invisible" sites. Line broadening from field inhomogeneity can be minimized by small sample volumes and high-speed magic angle spinning probes. Use of our 2mm fast MAS probe in conjuction with a special positioning device allows for fine calibration of the sample's vertical and angular position in the sweet spot area of the magnet, reducing field inhomogeneity linewidth to less than 50 ppb.

The 27Al spectra of 9Al₂O₃+2B₂O₃ obtained at different field strengths, including one from the hybrid magnet at 40 tesla.

At this point, magnetic field instability coming from power supply and temperature of cooling water becomes the dominant line broadening mechanism, contributing 3 ppm. Currently, we are working on methods to correct for such instability and further improve the spectra resolution. The advantage of high magnetic fields for high resolution NMR of quadrupolar nuclei is best illustrated in a figure to the right by 27Al spectra of 9Al₂O₃+2B₂O₃ (sample courtesy of D. Massiot, CNRS, Orlean, France). It shows field dependence of 27Al spectra from 14 to 40 Tesla, all acquired using magnets at the NHMFL. Even with the additional 3 ppm line broadening from the magnetic field instability, the spectrum at 40 T shows the best spectral resolution due to the reduction of the second-order quadrupolar effect.

References

1. Gan, Z.; Gor'kov, P.; Cross, T.A.; Samosan, A. and Massiot, D., Seeking for Higher Resolution and Sensitivity for NMR of Quadrupolar Nuclei at Ultra High Magnetic Fields, J. Am. Chem. Soc., 124 (20), 5634-5935 (2002), PDF
2. Gan, Z.; Gor'kov, P.; Massiot, D.; Butler, L. and Samoson, A., Solid State NMR of Quadrupolar Nuclei at Very High Fields, Annual Research Review, NHMFL, p.217 (2001)