A Decade of Experience With the UltraWide-Bore 900-MHz NMR Magnet

The ultrawide-bore (UWB) 900 MHz NMR magnet was commissioned in 2004. The magnet was conceived as part of the long range goal of NMR at fields in excess of 25 T that would require inner high temperature superconductor coils in the bore of a low temperature superconductor outer magnet of a sufficiently large bore. In order to address the combined interest in reaching 900 MHz while at the same time advancing the technology of large LTS NMR magnets, the decision was made to produce a 900 MHz magnet with an extended large bore to force the development of technology and for demonstration. Several advances in magnet technology were made in addition to the large bore in the areas of epoxy for impregnation and quench protection. During fabrication of the magnet, a joint between coil sections was possibly damaged, resulting in a large field drift in persistent mode. The cancelation of the field drift was initially a challenge but resulted in an excellent opportunity for the further development of drift compensation methods. Once the extended large bore was available, it was found to be increasingly of interest for unique NMR measurements. Since commissioning, the UWB magnet has played a central role in the NMR science program at the NHMFL. Major programs conducted in the magnet include biological solid state NMR both of uniformly oriented samples of membrane proteins that often represent drug targets for the pharmaceutical industry and magic angle sample spinning. The extended wide bore has allowed the magnet to be used for imaging at the high field of 21 T, including studies of high resolution ¹H images of adult rodents, ²³Na imaging in models ranging from single cells to in vivo rats to establish dynamic distributions of ionic sodium in pathological (stroke) and non-pathological (activation) conditions, and multi-modal nanoparticles used to track implanted cells as part of a cellular therapy for neurodegeneration. In addition ²³Na and Cl images of in vivo tumors in animal models have suggested important potential roles for evaluating pharmaceutical efficacy and other medical applications.