We have finalized the design of a full-scale tabletop 1.5-T/90-mm MgB2 “finger” MRI magnet system for osteoporosis screening based on our preliminary test results of small coils and superconducting joints. The magnet will operate in persistent mode at 10 K with an additional 5 K temperature margin. The magnet design satisfies the required specification of a field homogeneity of <5 ppm over a 20-mm diameter of spherical volume (DSV) after cool-down and energization, and a fringe field of <5 gauss at 0.5 m in radius from the magnet center. A cryocooled solid nitrogen (SN2) cryogenic system minimizes the heat input especially when the cryocooler is switched off to provide a vibration-free measurement environment during the MRI scanning. This paper covers designs of: 1) the main coils and an iron shield; 2) coil former structures; 3) cryogenic system 4) protection circuit; and analyses of 1) quench; 2) heat input into the cold mass; and 3) manufacturing tolerance sensitivity on field errors. The magnet system, to be constructed and tested in 2019, will in 2020 be equipped with a set of active-shielded gradient coils, an RF coil, and a 1.5-T MRI imaging system.
Acknowledgement: Research reported in this publication was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under award number R01EB022062.