Superconducting magnet, c 1990s.
© Science Museum / Science & Society Picture Library
Superconducting magnets can generate some of the strongest magnetic fields in the laboratory. They are able to do this because of the very highcapacity of superconductors for carrying electric current. Superconductors are materials which offer zero resistance to the pasage of an electric current when cooled to below a certain critical temperature. With early superconductors this was only a few degrees Kelvin (K), meaning that they had to be cooled using liquid helium, which is expensive and difficult to handle. In the 1980s, so-called high-temperature superconductors were discovered, allowing the use of liquid nitrogen instead of helium. Today, superconductors with critical temperatures as 'high' as 150 K (-123 C) have been developed.