Bespoke portable cryomagnet boosts University of Birmingham’s superconductivity research by allowing researchers to move easily between Europe’s x-ray and neutron facilities
Professor Ted Forgan, recent winner of the Mott Medal in physics, is a senior member of the Condensed Matter Physics group at the University of Birmingham.
He worked with Cryogenic Ltd on the design of a customised 17 Tesla cryomagnet which allows samples to be changed in situ. The equipment is used at neutron and x-ray facilities across Europe to analyse superconducting materials and the research has been published in a number of high-impact journals including Nature Physics.
The Condensed Matter Physicsgroup and their international collaborators analyse samples in high magnetic fields at temperatures near absolute zero to study the behaviour of superconductors and other materials.
The group wanted to use powerful neutron and x-ray beams to look at the behaviour of samples placed inside a strong magnetic field. In 2009, Ted Forgan, along with colleagues Gary Walsh, Elizabeth Blackburn and Alex Holmes worked closely with Marc Savey-Bennett, project engineer at Cryogenic, to design a new instrument to meet their specific research criteria.
Specifying a unique piece of equipment
Professor Forgan’s team had a number of specific requirements for the system. Firstly, samples of materials being analysed inside the equipment needed to be changed whilst maintaining the vacuum which keeps the magnet cold.
Working with neutrons requires a thick silicon window whereas working with x-rays requires a thin aluminium window. As the equipment was to be used in conjunction with both neutron and x-ray beams the ‘windows’ through which these passed needed to be changed easily.
Additionally, the equipment needed to be compact and robust in order to be transported to science facilities across Europe, such as the Institut Laue-Langevin in Grenoble, and also needed to be easily mounted onto different beamlines.
“We spoke to a few other suppliers about designing a bespoke system but none were able to produce exactly the equipment we wanted” explains Professor Forgan. “Cryogenic listened to us and weren’t daunted by our proposal. They gave us a quote quickly which was half the price of other suppliers. With squeezing of science budgets this was very good news! Being a small and agile company means they are able to produce something completely bespoke. Our team were welcomed to visit Cryogenic and discuss the detailed design several times during the process. The team at Cryogenic have been very helpful in responding to our ideas and making sure the equipment met our needs.”
Building a bespoke system
The Birmingham group worked with Cryogenic to design a sample load lock and a variable-temperature sample mount to go inside a liquid-helium-cooled 17 T magnet system. The load lock, constructed in Birmingham to be compatible with the magnet from Cryogenic, allows air to be pumped out of the space holding the samples, allowing a manipulator to quickly change the sample being analysed in situ, or also the cryostat windows, without losing the vacuum and warming up the cryomagnet.
This enables the group to perform several different experiments as they are able to change samples or go from one source of particles to another without the hassle and time taken up by losing the vacuum. The versatile equipment allows maximum use of valuable beam time. The cryomagnet and load lock have been described in a scientific paper published jointly with Cryogenic1.
Pure physics research
The 17 Telsa magnet is the most powerful of its kind being used in small angle scattering experiments. In order to understand the nature of superconductors, neutron or x-ray beams are passed through a sample and reflections of the beams at angles up to 10 degrees are detected.
Recent research using the system has allowed the team to publish papers in high-impact journals including Physical Review Letters2.
In one case the cryomagnet was mounted on to x-ray beamline BW5 at HASYLAB at the Deutsches Elektronen-Synchrotron in Hamburg. The research examined the behaviour of the high-temperature superconductor YBa2Cu3O6 y and found that it behaves differently under different magnetic fields, existing in two states. Under certain magnetic fields it deforms with a charge density wave and under others it becomes superconducting. The results of this were published in Nature Physics3 in 2012.
The unique nature of the equipment means that other scientists are keen to collaborate with the group whilst at international facilities and a number of national and international partnerships have been forged.
With complex equipment, it is not unusual to experiences glitches from time to time. In one case, whilst using the equipment at the Paul Scherrer Institutin Switzerland, the liquid helium level detector stopped working, making it impossible to run the experiment.
“We contacted Cryogenic and within a day they had sent a replacement that fitted our apparatus and we were back on track” says Professor Forgan. “This quick response was vital in allowing us to complete the research. It can take months to arrange a trip to a large science facility where you are allocated a finite number of hours of beam time. Without that support we would have missed the opportunity.”
The Birmingham group is now working with Cryogenic to modify the equipment. By installing a dilution refrigerator sample will be able to reach even lower temperatures. “We’ve got a great partnership with Cryogenic” he concludes, “they produced exactly what we want, and now they are helping us to extend its use even further.”
1 A. T. Holmes, G. R. Walsh, E. Blackburn, E. M. Forgan and M. Savey-Bennett (2012) A 17 T horizontal field cryomagnet with rapid sample change designed for beamline use, Review of Scientific Instruments 83, 023904.
2 E. Blackburn et al. (2013) X-Ray Diffraction Observations of a Charge-Density-Wave Order in Superconducting Ortho-II YBa2Cu3O6.54 Single Crystals in Zero Magnetic Field, Physical Review Letters 110, 137004.
3 J. Chang et al. (2012) Direct observation of competition between superconductivity and charge density wave order in YBa2Cu3O6.67,Nature Physics 8, 871–876.
Group website: www.cm.ph.bham.ac.uk