Superconductors carry record current flow

Prof David Caldwell and his team have produced samples of high-temperature superconducting yttrium barium copper oxide (YBCO) using a new technique for fabricating large, single grains of bulk superconductors.

Currently, producing YBCO superconductors is a complex and expensive process, as it must be done in a single grain in order to generate large magnetic fields, since boundaries between grains limit the flow of current in the bulk sample.

Similarly, microscopic defects within the material can impede the motion of magnetic flux lines and increase the flow of current through it. The distribution of these lines within a bulk superconductor has to be managed to maximise the flow of current and, therefore, the field.

‘Our process for making larger crystals is fairly spectacular,’ said Caldwell. ‘We have a sample and we have a seed crystal on the top. We physically melt the material and then we cool it down and a single grain grows from that crystal. What we’re left with is something like a hockey puck, around 4cm in diameter.’

As the material is melted, researchers at Cambridge experimented with adding different elements such as depleted uranium to the chemical composition. When cooled down, certain elements were shown to retain their integrity, allowing larger currents to flow through the material.

The team are now working with Boeing to develop the superconductors for fly-wheel energy-storage systems. But Caldwell believes applications could extend much further, to the production of cheaper equipment such as MRI imaging, magnetic bearings, motors and generators.

‘The new process means we can have materials produced as a batch and this significantly brings down costs,’ said Caldwell. ‘It’s getting very exciting now. I personally believe that in five years these materials are going to be generating income for the companies that sell them.’