Breaking the world superconductor magnetic field record

Mark Ainslie

Fellow in Engineering Dr Mark Ainslie and other members of the Bulk Superconductivity Group in the Department of Engineering have just broken the world record for the strongest trapped magnetic field in a bulk high-temperature superconductor.

The team, which is led by Professor David Cardwell, has broken an 11-year record by trapping a 17.6 Tesla magnetic field. The previous record was held by a group in Japan, and was 17.24 Tesla.

What makes the new record so remarkable is that it was achieved using high temperature superconductors that were made relatively simply. The 25 mm diameter samples were created with a well-established melt processing method and reinforced with a shrink-fit stainless steel ring.

Superconductors are materials that can carry an electric current with little or no resistance below their so-called critical temperature. The first superconductors that were discovered only became superconducting close to absolute zero (−273ºC). For over eighty years they were restricted to metals and alloys that had critical temperatures up to 23 Kelvin (–250ºC).

High temperature superconductors were discovered in 1987 and exhibit superconducting properties above 77 Kelvin (−196 ºC). This makes them more viable for practical applications because the materials can be cooled by liquid nitrogen. Liquid nitrogen is inexpensive (cheaper than milk), easy to use and store, and readily available.

When a strong magnetic field is applied to the bulk form of a superconductor (which looks like an ice hockey puck), a large circulating current is induced in the material. Because the superconductor has no resistance, this current continues to circulate (as a so-called 'persistent current') even when the external magnetic force is taken away. The current produces a strong magnetic field above the superconductor, so the superconductors can be used as permanent magnet equivalents.

As an Electrical Engineer, Mark is particularly interested in these strong superconducting bulk magnets because they can be used in practical applications like motors. A stronger magnet means that motors can be made smaller and still provide the same power, or can be more powerful and efficient at existing sizes. For an overview of Mark's work on superconductors, see Current research.

The research paper is published in Superconductor Science and Technology:

J. H. Durrell, A. R. Dennis, J. Jaroszynski, M. D. Ainslie et al., A trapped field of 17.6 T in melt-processed, bulk Gd-Ba-Cu-O reinforced with shrink-fit steel, Superconductor Science and Technology 27 (2014) 082001

26 June 2014