A Superconducting Permanent Magnet Motor has been built at Cambridge University’s Engineering Department in collaboration with Magnifye Ltd.
Magnifye is developing the technology to produce the strongest permanent magnets in the world. Using rare earth superconductors Magnifye’s technology enables these to be magnetised to fields orders of magnitude greater than that available from ordinary permanent magnet materials such as NdFeB and SmCo. Magnifye has developed a heat engine which converts thermal energy into currents of millions of amps. The thermal energy is used to create a series of magnetic waves which progressively magnetise the superconductor much in the same way a nail can be magnetised by stroking it over a magnet.
As long as the superconductor stays cold, the currents will flow uninterrupted, providing powerful, stable, shapeable magnetic fields for a wide range of applications. These powerful magnets can be small enough to fit in the palm of the hand and large enough to power a train or a cruise liner.
Engineers at the University of Cambridge have also used new techniques to manufacture high-temperature superconducting materials, producing samples that can carry record quantities of electrical current for their type and size. he breakthrough has improved the effectiveness of yttrium barium copper oxide (YBCO) and a related family of superconducting materials. It raises the prospect of more powerful and affordable samples that could have huge benefits in a number of fields.
At present effective superconductors are often expensive and difficult to mass-produce. The Cambridge research could be a step towards resolving this, by providing the basis for the development of more powerful samples that can be manufactured using a commercially compatible process.
That would drive down the production costs of machines that rely on the materials. MRI scanners, for example, which can cost around £1.5million each, could eventually become a common sight in GP’s surgeries, helping to improve accurate detection and diagnosis of problems ranging from twisted knees to brain tumors.
The Cambridge team have developed a technique to manufacture large single grains of bulk superconductors that involves initially heating the material to a temperature of 1,000 degrees C, causing it to part-melt. In a series of experiments, various elements, such as depleted uranium, were then added to the chemical composition of the superconductor to generate artificial flux pinning sites within the single grain.
When the material cooled and reformed, these added materials retained their integrity and formed physical obstacles that form direct the motion of magnetic flux lines, enabling larger currents to flow.
In addition, the team developed a technique for fabricating large, single grains of bulk superconductors in air, using a new type of seed crystal that they have also patented, which enables much more scope for optimising the partial-melt process. Together, these techniques led to the production of samples far more powerful than those fabricated by more standard techniques, which exhibited record energy densities and magnetic fields for their size.
“The properties these samples exhibit could in time offer huge commercial potential by improving or reducing the weight and size of applications such as energy storage flywheels, magnetic separators, motors and generators,” Professor Cardwell added.
LS Cable, a South Korean company based in Anyang-si near Seoul, has ordered three million metres of superconducting wire from US firm American Superconductor in Devens, Massachusetts. LS Cable will use the wire to make about 20 circuit kilometres of cable as part of a programme to modernize the South Korean electricity network starting in the capital, Seoul.
Jason Fredette, managing director of corporate communications American Superconductor expects that other nations will soon be turning to YBCO as a superconductor. “China is looking at a project of is own, so the market is really finally starting to develop,” he says. The United States is also interested in using superconducting cables, supplied by LS Cable, to connect the country’s three main power networks.
American Superconductor makes its wire using a core of YBCO coated with copper, stainless steel or brass to provide strength. Yttria (Y2O3) nanodots dispersed through the YBCO layer stabilize the current flow, improving the current carrying capability of the wire by helping to control the magnetic fields in and around the wire
The top seeded melt growth (TSMG) process has been used extensively to fabricate large, single grain Y–Ba–Cu–O (YBCO) superconductors that can trap large magnetic fields of up to 17 Tesla at 29 K in a two sample arrangement.
Superconductive electronics has to be cooled to very low temperatures. Whereas this was a bottleneck in the past, cooling techniques have made a huge step forward in recent years: very compact systems with high reliability and a wide range of cooling power are available commercially, from microcoolers of match-box size with milli-Watt cooling power to high-reliability coolers of many Watts of cooling power for satellite applications. Superconductive electronics will not replace semiconductor electronics and similar room-temperature techniques in standard applications, but for those applications which require very high speed, low-power consumption, extreme sensitivity or extremely high precision, superconductive electronics is superior to all other available techniques.