An investigation into a flux-pumped high-temperature superconducting MRI system

Abstract

Since the discovery of superconductivity in 1911, numerous applications have been studied including high-field magnets, Magnetic Resonance Imaging (MRI) magnets, fusion magnets, superconducting fault current limiters, energy storage devices, and many others. Among all of the applications, MRI magnets make up the major part of the commercial application of superconductors. More than 80 % of MRI scanners around the world use superconducting magnets. However, nearly all existing MRI scanners use low-temperature superconducting (LTS) magnets. The discovery of high-temperature superconductors (HTSs) in the 1980s opened new doors for researchers as the newly discovered materials could operate at higher temperatures with higher critical currents and fields. In the last two to three decades, the production of HTS tapes has increased significantly making them easily accessible for researchers at a reasonable cost. HTS is slowly making its way into high-field magnet applications, fusion magnets, and MRI magnets. Thus far a fully HTS MRI scanner is not available commercially although various research groups are doing research. HTS magnets can be crucial in developing a truly accessible, portable, and mobile MRI scanner. The work in this thesis focuses on the design of an HTS magnet, gradient coils, and a cryostat for a prototype of a fully HTS MRI instrument. In addition to the design of the magnet, this work also focuses on the thermal analysis of the cryostat. The in-house design and fabrication of gradient coils for the MRI instrument is another important aspect of this work. The most important and innovative part of the work is the incorporation of a flux pump in the system. Superconducting magnets operate in persistent current mode once they have been energized. Generally, conventional power supplies are used to energize the superconducting magnets. The losses associated with these bulky leads are unavoidable; as a result, these current leads are relatively less efficient. A flux pump is an alternative to conventional power sources and bulky copper leads. Flux pumping is an electrically contactless method to energize superconducting magnets. There is no direct electrical contact with any external power source, eliminating the need for bulky current leads. So far flux pumps have not been used commercially with MRI magnets. This work can be a stepping stone toward the realization of a compact and mobile fully HTS MRI scanner powered by an inbuilt flux pump.