A team led by Dr John Durrell, University Lecturer in the Bulk Superconductivity Group, has demonstrated a portable superconducting magnetic system that can act as a high-performance substitute for a conventional permanent magnet and can attain a 3-tesla level for the magnetic field. The work is published in Applied Physics Letters.
Before we were using conventional superconducting magnets to charge our bulks. This will make access to these high fields cheaper and more practical.John Durrell
Durrell said his team’s work in large part evolved from the innovative findings of University of Houston physicist Roy Weinstein, who has shown how conventional electromagnets and pulsed field magnetization can be used to activate superconducting magnetic fields which are ‘captured’ and sustained as part of a superconductive arrangement. This avoids the requirement for large expensive superconducting magnets to “activate” such portable systems. Also key, Durrell pointed out, is that his team capitalised on other new and cheaper technologies, especially for cooling.
“The leap with advances in cryogenics, allows you to do interesting things in other areas, too,” Durell explained. “There is a lot coming together to make this possible.” While large industrial-size superconducting systems do generate a 20-tesla magnetic field, Durrell’s 3-tesla magnetic field is new for a portable system.
Durrell and his team were curious about what they could do as they looked at Weinstein’s work just a few years earlier. Weinstein demonstrated that with conventional external electromagnetic pulsing of a medium, it was possible to ‘capture’ a magnetic field in a superconductor using a much smaller external magnetic field than previously thought possible. The Weinstein investigation used yttrium barium copper oxide (YBCO) doped with uranium and subject to an irradiation treatment. Durrell’s team looked for a less expensive material and chose gadolinium barium cuprate, without uranium doping.
Difan Zhou, team investigator and lead author of the paper, came up with the idea of extending Weinstein’s findings and the research, which took just short of two years to do, has paid off.
“It was a surprise to us that we managed to see in a not-quite-so-cutting-edge-material the same giant flux leap effect as Roy Weinstein demonstrated,” Durrell said. “The key thing that made this possible is that we have looked at what Roy has done to get it to work but for this kind of portable system. Before we were using conventional superconducting magnets to charge our bulks. This will make access to these high fields cheaper and more practical.”
Advances in cheaper, more efficient cooling – the cryogenic system – were also key for Durrell and the team’s research. For both the magnetic field charging and sustaining phases, it is necessary to keep the superconducting sample cool or else the superconductivity gives out. Recently, the private sector has come up with cryogenic systems that are cheap and light, and Durrell used a cooling system from US firm Sunpower. According to Durrell, this lightness and relative low cost could make portable superconductivity in various products a real possibility.
Durrell and his team are planning for more testing for more magnetic power and overall efficiency. They have received significant support from Boeing for this investigation, and Durrell feels it is a strong example of what a company and an academic lab can do when they team up for basic research.
A portable magnetic field of >3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors: http://dx.doi.org/10.1063/1.4973991