Title: Large Bulk (RE)BCO superconducting magnets for desktop NMR/MRI
Funder: Engineering and Physical Sciences Research Council

Abstract: NMR and MRI are techniques that use the interactions of atoms with external magnetic fields to look inside materials, objects and organisms to study their composition (NMR) and provide images (MRI). They are used very widely in scientific research, medical research and in industry and medicine. Put simply, the stronger the magnetic field available the better these techniques work. Unfortunately, obtaining large magnetic fields (typically 20 -30 times strong than a fridge magnet) generally requires expensive magnets, which are usually wound from long lengths of superconducting wire. It would be ideal to be able to produce these very large magnetic fields in a much simpler fashion to provide convenient and cheap desktop systems. Making these systems widely available and cheaper would allow more scientists, engineers and medical researchers to have access to this equipment, and to use it more often. The importance of this proposed project is underlined by the active participation and practical help offered by our three industrial partners. We are proposing to use ceramic bulk (in disc- or ring-form) superconductors, rather than complex solenoidal coils made from superconducting wire. The three main challenges that must be overcome to do achieve this are (i) making bulk superconductors of sufficient size and uniformity, (ii) making the magnetic field they produce highly uniform, and (iii) developing a practical way of charging bulks samples with magnetic field. To address the first two challenges the Cambridge group, with extensive experience of the fabrication and manufacture of these bulk superconductors, is going to partner with the Oxford group, who have experience of using advanced microscopy to look carefully at the fine details of the manufacturing process. To magnetise the bulk superconductors, we propose to discharge, over a period of several milliseconds, the energy stored in a bank of capacitors into a conventional coil magnet made of copper. Such a copper coil would overheat and melt if were to generate a large magnetic field continuously. However, using this pulsed field magnetisation technique, we can achieve the required field over a short period of time, but long enough to allow the bulk superconductor to "capture" the magnetic field. We will consider the project successful if we can replace the conventional, permanent magnet of an existing NMR system, provided by our industrial partner, with our prototype bulk superconductor based system and demonstrate that it operates effectively at the proton resonance frequency of 200 MHz, rather than at 90 MHz, which is typical of existing permanent magnet systems and a limiting feature of this technology.

Lay abstract: The primary goal of this project is to enable the construction of a bulk superconductor-based magnet suitable for small scale desktop NMR and/or MRI, with the following main objectives: 1) To develop new processing techniques to allow the growth of large (90 mm in diameter) bulk superconductors required for the fabrication of superconducting rings with a bore size of 54 mm; 2) To achieve trapped fields with a homogeneity of better than 10 ppm; 3) To develop a system to allow the charging of the bulk magnets using pulsed copped coils; 4) To demonstrate the operation of a 200 MHz NMR (4.7 T) system where the field is provided by pulse-charged bulk superconductors.

Research activity codes: 2.6 RESOURCES AND INFRASTRUCTURE (AETIOLOGY);4.5 RESOURCES AND INFRASTRUCTURE (DETECTION)
Health categories: GENERIC HEALTH RELEVANCE