A 1.5-T superconducting solenoid-dipole magnet for a magic-angle spinning field

点击翻译按钮获取中文摘要

Phase 1 of this 2-phase program has two specific aims: 1) successful completion of a magic-angle-field (MAF) magnet of a significant field strength with an NMR-quality field homogeneity for slow MAS (magic-angle-spinning) MRI/NMR; and 2) application and demonstration with the proposed system of an innovative cryogenic system suitable for a superconducting magnet spinning in Phase 1 slowly (~0.1 Hz) and in Phase 2 at 6 Hz. Unlike a conventional NMR or MRI magnet that has a field vector of NMR quality directed only in one axis, an MAF vector may be decomposed into two field vectors, one directed in one axis and the other in the direction normal to the first axis. The best, and perhaps the easiest, way to ensure an NMR-quality field directed at an angle of 54.74o from the magnet axis (also the rotation axis) is to ensure independently an NMR-quality field generated by each of the coils comprising an MAF magnet. This is the crux of our innovative design concept to build a successful superconducting MAF magnet: a combination of an axial z-field solenoid coil and an x-axis field dipole coil, each generating an NMR-quality field of a specific strength. By adjusting each coil's field strength, we will be able to achieve with this Phase 1 magnet both requirements of field strength (here 1.5 T) and angle (54.74o). With this magnet, for the very first time, MAS NMR/MRI sciences will have a superconducting MAF magnet that generates an NMR- quality field of significant strength, e.g., 1.5 T >> 36 gauss (the previous high by the UC Berkeley group), operated in persistent mode. Another notable significance is an innovative cryogenics design applied to this magnet (also to used in Phase 2). Instead of operated in a bath of liquid helium (LHe), the magnet will be immersed in solid nitrogen (SN2). (In phase 2,the magnet will be housed in a cryostat which will rotate at 6 Hz.) This all-solid cold body ameliorates thermo-fluid issues associated with LHe under rotation. Also, the presence of SN2 in the cold body not only ensures a more uniform temperature throughout the windings but also provides a large thermal mass, enabling the magnet to maintain its operating field over a time period even when the primarily cooling source (LHe in Phase 1) is shut off. In summary, the successful completion of this 2-phase program will open new opportunities in MAS NMR/MRI sciences, which in turn will open new avenues to modern instrumental analysis, ultimately leading to novel non-invasive biomedical tools for analysis, diagnosis, and disease prevention.