Engineering news
Researchers from Cambridge University have developed the world's strongest high temperature superconductor in an experiment they say brings their widespread commercial use in a range of sectors a step closer.
The team of engineers “trapped” a magnetic field the strength of 17.6 Tesla – roughly 100 times stronger than the field generated by a typical fridge magnet – inside a golf ball-sized lump of gadolinium barium copper oxide (GdBCO), a material normally as brittle as fine china.
The experiment beats the previous world record, which was set by a Japanese university more than ten years ago, by 0.4 Tesla.
Research lead, Professor David Cardwell, from the University of Cambridge’s engineering department, said: “This work could herald the arrival of superconductors in real-world applications.
“In order to see bulk superconductors applied for everyday use, we need large grains of superconducting material with the required properties that can be manufactured by relatively standard processes.”
High-temperature superconductors could potentially be used in a range of applications, including flywheels for energy storage, as “magnetic separators” in mineral refinement and pollution control, and in high-speed levitating monorail trains.
Conventional superconductors, such as those used in MRI scanners and complex physics experiments, need to be cooled close to absolute zero (–273 °C) before they superconduct. But high temperature superconductors, such as GdBCO, superconduct above the boiling point of liquid nitrogen (–196 °C), which makes them relatively easy to cool and cheaper to operate.
The current carried by a superconductor also generates a magnetic field, and the more field strength that can be contained within the superconductor, the more current it can carry. State of the art, practical superconductors can carry currents that are typically 100 times greater than copper, which gives them considerable performance advantages over conventional conductors and permanent magnets.
The superconductor was made by fabricating a stack of two silver-doped GdBCO superconducting bulk samples, each 25 mm in diameter, using top-seeded melt growth and reinforced with shrink-fit stainless steel. This relatively straightforward and inexpensive technique offers the prospect of easy access to portable, high magnetic fields without any needing a sustaining current source.
The major challenge with the superconductor material is its brittleness when fabricated in the form of sintered ceramics. A strong magnetic field normally causes them to explode.
In order to trap, the magnetic field, the researchers modified both the microstructure of GdBCO to increase its current carrying and thermal performance, and reinforce it with a stainless steel ring.
The lines of magnetic flux in a superconductor repel each other strongly, making containing such a large field difficult. But, by engineering the bulk microstructure, the field is retained in the sample by so-called ‘flux pinning centres’ distributed throughout the material. Dr Yun-Hua Shi, who has been responsible for developing the melt process fabrication technique at Cambridge for the past 20 years, said: “The development of effective pinning sites in GdBCO has been key to this success.”
A number of applications are being developed by the Cambridge team and its collaborators, and it is anticipated that widespread commercial applications for superconductors could be seen within the next five years.