Large Bulk (RE)BCO superconducting magnets for desktop NMR/MRI

Lead Research Organisation: University of Cambridge
Department Name: Engineering


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.

Planned Impact

The aim of this project is to lay the foundation to open up a whole new market segment for desktop MRI and NMR systems utilising magnetic fields of up to 5 T. Existing systems either use large and bulky room size superconducting solenoids and are expensive (>£1m) or sacrifice performance by employing much cheaper permanent magnets [1]. Our project would therefore make a direct and positive economic contribution in a field where UK companies, including Oxford Instruments and Siemens Healthineers, both of which are partners in this project, are sector leaders [2]. The NMR market has been predicted to reach over $2.5 billion by the mid 2020s [3] and that of the MRI market $5 billion [4].
Reducing the cost and size of these instruments will have a broader societal impact, making the technology, as well as the analysis, more affordable for end-users. In addition, the increased field offered by bulk superconducting magnets will allow improvements in performance, from 40-90 MHz typical of permanent magnet systems [5] to 200 MHz, increasing throughput and widening the range of applications for these cheaper systems.

Our proposal has been developed with companies that make systems using these technologies. This means they will be able to advise us at every stage of the project to make sure that our focus is relevant to the ultimate exploitation of the technology. This also means that, if successful, there will be a clear route from laboratory to factory for the progress we demonstrate.
This project targets a bore size suitable for research, rather than medical diagnostic work. Nonetheless, if we successfully overcome the limitations of sample size, solenoids based on bulk superconductors could find a role in Extremity MRI [6]. These are compact systems that reduce the load on expensive full size systems by providing imaging of limbs. This is of increasing importance as MRI becomes a more heavily used technique, in the NHS there has been an over 200% increase in demand over a 10-year period [7].

The availability of larger, high quality, bulk superconductors that we propose to develop would benefit the wide range of potential applications for bulk superconductors. Those identified, besides NMR and MRI , in our recently published roadmap for the application of bulk superconductors[8] include compact high power density motors for electric aircraft and road transport, large magnetic fields for drug targeting and magnetic shielding systems.

[2] Melhem Z 2011 Materials UK Prelim. Review, Superconducting Materials and Applications: A UK Challenge and an Opportunity
[8] Durrell et al., Superconductor Science and Technology, Volume 31, Number 1


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Description Due to the Covid-2019, there has been limited access to the lab in 2020-21, which means only 60% of the work has been completed.

1. A study on the stacking of two single grains exhibiting different trapped fields at their top and bottom surfaces has been performed and completed. The results show that the best high and most uniform trapped field of the stack of two samples is achieved by placing the two bottom surfaces (which are usually those with lower and non-uniform trapped fields) in intimate contact in the middle of the stack.

2. A further improved and stabilised the melt process has been developed. This process involves wet-ball mixing to increase the uniformity of the mixed precursor powder to improve the reliability of the crystal growth and uniformity of the superconductivity within the bulk single grains.

3. A method that allows the growth of ring-shaped single grains directly has been developed to improve the uniformity of the superconducting properties.

4. The superconducting properties of single grains containing different rare-earth elements (Gd and Eu), different sources of supply and the effects of the Ag addition has been investigated. The results show that adding Ag improves the superconducting properties of the single grain, including the trapped field, despite the fact that Ag is not superconducting. Research in this area is continuing.

5. Multi pulse-magnetisation of a relatively large numbers of bulk and ring samples has been used to demonstrate there is no clear correlation between the trapped field obtained by field-cooling by pulse-magnetisation. The thermal conductivity of the assembled composite single grain, however, is most likely a dominating factor in determining the final trapped field.

6. The intrinsic uniformity of the superconducting properties of single grain (RE)BCO materials has been further studied. For the first time, the distribution of the Jc-B at a facet line has been measured and compared with the distribution of Jc-B in the a/b direction. In general, and significantly, the facet lines exhibit higher Jc-B.

7. A variety of shapes of bulk, single grain material, such as cylinders, rings 41OD16ID (8 of 10), square and triangular geometries have been fabricated successfully. The work for assembling the samples for designs A and B in the proposal is in progress.
Exploitation Route The results of the study on the stacking of two single grains will help the scientific community understand the use of one type of an assembly of single grains. The improved trapped field obtained and uniformity in the resultant composite bulk compared to a monolithic bulk superconductor of the same diameter will help design the assemblies for bespoke, high field applications.

The processing technique developed to allow the growth of ring-shape single grains directly what the potential to save materials and improve superconducting properties (more analysis is being performed).
Sectors Energy,Healthcare,Transport

Description Can Superconductors 
Organisation Can Superconductors
Country Czech Republic 
Sector Private 
PI Contribution The investigation of parallel processing techniques for bulk single grain superconductors.
Collaborator Contribution Play the fundamental role in understanding the properties of performance of bulk superconductors fabricated from a variety of rare earth elements.
Impact The development of an improved melt process for bulk superconductors that yields better trapped field and greater potential for engineering applications.
Start Year 2006
Description Siemens 
Organisation Siemens AG
Department Siemens plc, Keele
Country United Kingdom 
Sector Private 
PI Contribution We provide samples for Siemens to do some measurements using their equipment.
Collaborator Contribution Siemens is interested in the applications of bulk materials in motors. Our research results will provide better understanding.
Impact multi-disciplinary
Start Year 2016