A design flux injector for NMR superconducting magnets : results of operation with superconducting insert cells

Abstract

It has been known for some time that high-temperature superconductors (HTS) are critical for the construction of NMR magnets generating 1 GHz and above. Such systems generally require an HTS insert to be placed in the inner high-field region of a low temperature superconducting (LTS) magnet. Among the problems in the presently available HTS technology are splice resistance and index dissipation, which make it essentially impossible for HTS to operate in persistent mode. Unless operated in driven mode with a very stable power supply, the HTS insert generally cannot achieve NMR-quality temporal stability. Another option, proposed by Iwasa, is by the use of a digital flux injector (DFI), which is a transformer type of device that can inject a quantified amount of magnetic flux into a "slightly" resistive magnet to compensate the energy dissipation over time. Previous work at the Francis Bitter Magnet Laboratory (FBML) showed a prototype DFI operate successfully with an LTS insert magnet and demonstrated the basic concepts of this alternative approach. Based on the prototype, the first full-scale DFI has been designed, built and operated with an LTS insert magnet and an HTS insert magnet separately. The design process, operation procedure and experimental results are the main topics of discussion in this thesis.