Superconductivity, where electrical currents travel unhindered through a material, has many practical uses. It is used in applications extending from MRIs in hospitals to the cavities of particle accelerators. However, practical exploitation of superconductivity also presents many challenges.
The challenges are perhaps greatest for researchers trying to integrate superconductivity into small, portable systems. Cambridge University superconductivity expert John Durrell and his team demonstrated that a portable superconducting magnetic system, essentially a high-performance substitute for a conventional permanent magnet, can attain a 3-tesla magnetic field. The work is published in Applied Physics Letters.
Durrell said his team's work in large part evolved from the 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 that are “captured” and sustained as part of a superconductive arrangement. This avoids the need for large, expensive superconducting magnets to “activate” such portable systems. Also key, Durrell pointed out, is that his team capitalized on other new and cheaper technologies, especially for cooling. While large industrial-size superconducting systems generate a 20-tesla magnetic field, Durrell's 3-tesla magnetic field is new for a portable system.
Roy 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 Cuprate doped with Uranium and subjected to an irradiation treatment. Durrell's team looked for a less expensive material and chose Gadolinium Barium Cuprate, without Uranium doping. Team investigator Difan Zhou 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-cuttingedge-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 the 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. Durrell used a cooling system from Sunpower Inc. of Athens, OH.
The total effect of bringing together these new technological opportunities, Durrell pointed out, is “essentially a better, portable permanent magnet — one with a 3-tesla rather than 1-tesla magnetic field. The obvious interest in that is that you could use that to make a smaller and lighter motor.”
Durrell and his team are planning to test for more magnetic power and overall efficiency. They received significant support from The Boeing Company for this investigation.
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