A bulk MgB2 magnet demonstrator for biomedical applications

Lead Research Organisation: University of Oxford
Department Name: Materials

Abstract

Bulk superconductors are dense pellets of superconducting material that can be used as compact permanent magnets. Harnessing the ability of these materials to produce considerably higher magnetic fields than conventional ferromagnets will be transformative for a wide range of devices for biomedical and energy applications. These materials have the added safety benefit that the magnetic field can be switched off. However, their enormous potential has yet to be realised in commercial devices for a number of reasons. High temperature superconducting bulk materials, such as YBCO, have the ability to produce very high fields, but they are expensive to produce, cannot be made with large diameter and suffer from relatively poor sample-to-sample reproducibility. Lower temperature superconductors like magnesium diboride (MgB2) are much cheaper and easier to process, but they require expensive and bulky cooling systems. Furthermore, all bulk samples present the additional challenge that they initially need to be magnetised using an external field.
This project involves designing and building a desktop sized magnet to demonstrate that these challenges can be overcome in practical devices by integrating state-of-the-art cryogenics and pulsed magnetisation systems with high performance, low-cost MgB2 superconductor. A bespoke cryostat will be developed by our team at the Rutherford Appleton Laboratory, who are experts in compact and efficient cryocoolers for space applications and coils will be incorporated into the cryostat, enabling the bulk superconductor to be magnetised in situ. The nano-scale structure of the MgB2 material will be optimised for operation at higher temperatures using a novel powder processing strategy, and large, high density samples will be manufactured using the commercial diamond presses at Element Six.
Preliminary experiments will be carried out using the demonstrator magnet, to assess the feasibility of using this technology for magnetically targeted drug delivery, with collaborators at the Institute of Biomedical Engineering in Oxford. More complex shapes of superconductor will be explored, with a view towards developing more sophisticated devices for selected applications such as MRI in future projects.

Planned Impact

The UK is recognised world-wide for its strength in superconductivity research, magnet innovation and cryogenics engineering [1]. The MRI/NMR industry, which is dominated by the UK, provides about 90% of the 4Bn Euro global superconductivity market, with over 30,000 MRI scanners installed in hospitals worldwide. These instruments are based on mature low temperature superconducting (LTS) wire technology and operate at 4K. Of increasing importance are a series of emerging technologies that can be best realised using bulk superconducting magnets operating at temperatures over 20K. These applications cut across a range of different sectors including healthcare, electric transport and renewable energy. However, these superconductors are at a much lower technology readiness level, so research investment is required now to develop practical materials and systems in order to accelerate impact and keep the UK at the forefront.
The principal aim of this project is to build a compact and low-cost demonstrator device using MgB2 superconducting bulks capable of producing higher magnetic fields than conventional rare-earth ferromagnets. Our motivation is to revolutionise important therapeutic and diagnostic medical devices by providing easy and cheap access to higher magnetic fields in a clinical and laboratory setting. These applications include magnetic drug targeting (MDT), magnetic cell separation, and compact MRI machines.
MDT has significant potential advantages over non-specific therapies for treating diseases like cancer and arthritis, allowing lower doses and minimising side-effects by concentrating the drug at the target site [2]. It is also a promising method for treating serious neurological disorders such as brain tumours and Alzheimer's disease, by enhancing the transport of drugs across the blood-brain barrier [3]. Other exciting potential applications for this technology include targeted gene therapy [4] and radionuclide therapy [5]. This research is at a fairly early stage, and it is an open question whether magnetic targeting can be used effectively in humans [6]. We will work closely a research group at the Institute of Biomedical Engineering in Oxford to demonstrate that the higher fields achieved using superconducting bulk MgB2 magnets improve the effectiveness of magnetic trapping under conditions relevant to the human body. This will open up opportunities for accessing a greater range of target sites including wider vessels and locations deeper inside the human body.
MRI is an increasingly important medical diagnostic tool, with the NHS reporting a 220% increase in the number of MRI scans over a ten year period, leading to long patient waiting times [7]. Introducing compact, low-cost MRI machines to complement the traditional whole-body scanners is an attractive option for meeting this increasing demand [8]. Current generation MRI machines are very expensive and bulky owing to their reliance on large, low temperature superconducting solenoid magnets. The large volume of liquid helium cryogen needed to cool the magnets is not only inherently dangerous, but concerns over the global supply of helium is leading to price increases and uncertainty. There is a considerable market and appetite for smaller, cheaper units for diagnosing common limb injuries [8], to alleviate pressure on existing whole-body scanners. Replacing permanent magnets with bulk superconductors in compact MRI machines would improve sensitivity, leading to the better image quality desired by doctors and higher patient throughput.

[1]Melhem Z 2011 Materials UK Prelim. Review, Superconducting Materials and Applications: A UK Challenge and an Opportunity [2]Pankhurst 2003 J Phys D 36 R167 [3]Patel 2010 J Pharm Parm Sci 13 536 [4]Hasenpusch 2012 Pharm Res 29 1308 [5]Sofou 2008 Int J Nanomedicine 3 181 [6]Owen 2015 Interface Focus 5 20150001 [7]https://www.england.nhs.uk/statistics/ [8]Trueland 2014, Health Service Journal supplement.

Publications

10 25 50
 
Description What were the most significant achievements from the award?
We successfully managed to improve the current-carrying performance at high magnetic field of magnesium diboride bulk samples made by ex situ processing without introducing a degradation in the critical temperature of the superconductor. Important developments in the MgB2 sample processing in Oxford included (a) developing a new method to achieve a nanoscale distribution of secondary phase precipitates that improve critical current density by acting as flux pinning centres by adding insoluble Y2O3, dissolving it in the MgB2 through high energy ball milling of the powders and then precipitating it out as YB4 during the consolidation process; (b) using Mg powder additions to improve sintering at lower temperatures, reducing coarsening of the microstructure; (c) first fabrication of ring-shaped samples using the field assisted sintering technique (without machining) that can be assembled to make a pseudo solenoid magnet. In addition we have improved understanding and awareness of how the inhomogeneous microstructures in MgB2 bulk samples affect the standard method for extracting critical current density from magnetisation measurements and have shown that great care must be taken when analysing flux pinning mechanism using standard pinning force analysis methods on samples with this type of microstructure. The work in Cambridge on the magnetisation of MgB2 bulk samples to turn them into permanent magnets using pulsed field charging found that improving the cooling architecture increases the flux trapping capabilities and alters the flux motion during charging. These improvements lead to the largest trapped field (0.95 T) for a single MgB2 bulk sample magnetised by a solenoidal pulsed field magnet. In addition, the improvement in controllability of the pulsed charging rig developed in Cambridge led to findings that the shape of the pulse and the series of pulses used play a key role in determining the final trapped field. Pulse charging of a three ring stack successfully managed to trap a magnetic field of 2.04T at 20K although.

To what extent were the award objectives met? If you can, briefly explain why any key objectives were not met.
The main objectives concerning development of processing techniques and microstructural optimisation as well as setting up a suitable system for pulse field charging were met. However, there were many delays and unanticipated difficulties in the design of the liquid neon portable cryostat at STFC (not least associated with Covid delays). This meant that we were unable to test the MgB2 samples in the bespoke cryostat, which was unfortunate. We performed preliminary magnetic separation demonstrations using a REBCO bulk in a different cryostat in Cambridge, and this work will be continued in a subsequent project, with the aim of producing a video for outreach and PER activities.

How might the findings be taken forward and by whom?
The work on MgB2 bulk processing and microstructural optimisation is being taken forward in Oxford by a PhD student working with Epoch wires on joints for MgB2. The pulsed field charging findings are being taken forward in the ongoing EPSRC grant on REBCO bulk samples for NMR/MRI.
Exploitation Route Insights and improvements to pulsed field magnetisation of MgB2 and REBCO will be of use to all of the bulk superconductivity community as this remains the only practical portable method of magnetising bulks. The insights into MgB2 processing will be used by us (on our ongoing joints project) and other research groups working on bulks and wires.
Sectors Energy,Healthcare

 
Description Large Bulk (RE)BCO superconducting magnets for desktop NMR/MRI
Amount £784,207 (GBP)
Funding ID EP/T01539X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2020 
End 02/2024
 
Title Design and characterisation of ex-situ bulk MgB2 superconductors containing a nanoscale dispersion of artificial pinning centres 
Description Contains the raw PPMS (superconducting property measurement) data and XRD scans plus image files of the electron microscopy results (STEM and TKD) presented in Matthews, G., Liu, J., Grovenor, C., Grant, P., & Speller, S. (2020). Design and characterisation of ex-situ bulk MgB2 superconductors containing a nanoscale dispersion of artificial pinning centres. Superconductor Science and Technology, 33(3). 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact First demonstration of using the 'ODS' concept to improve superconducting performance of MgB2 superconducting bulk samples without degrading transition temperature. 
URL https://ora.ox.ac.uk/objects/uuid:d282e2e5-b952-491b-9e54-b6cbfbbe13f0
 
Title Effect of the sintering temperature on the microstructure and superconducting properties of MgB2 bulks manufactured by the field assisted sintering technique 
Description Raw PPMS magnetisation data and XRD data files associated with publication: G A B Matthews et al 2020 Supercond. Sci. Technol. 33 054003 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
Impact Materials processing improvements that have enabled the manufacture of higher performance bulk superconductors and novel ring superconductors. 
URL https://ora.ox.ac.uk/objects/uuid:b8aa6e71-8960-47bc-a186-aec73338efb2
 
Description Dr Fritsch, Germany 
Organisation Dr Fritsch
Country Germany 
Sector Private 
PI Contribution Knowledge and expertise in MgB2 processing and factors affecting superconducting properties. Measurement of the superconducting properties and microstructural characterisation of materials made at Dr Fritsch.
Collaborator Contribution Expert knowledge of the FAST technique for processing advanced materials. Design and fabrication of moulds specifically for manufacturing novel MgB2 tubes. Processing of numerous tube samples using their state of the art FAST machines. Supplying raw materials for the fabrication of tubes.
Impact Set of tube samples have been delivered and the properties of stacks of tubes for permanent magnet applications have been assessed. A paper is in preparation for imminent publication.
Start Year 2019