A novel magnet half the size of a cardboard toilet tissue roll usurped the title of “world’s strongest magnetic field” from the metal titan that had held it for two decades at the Florida State University-headquartered National High Magnetic Field Laboratory.
And its makers say we ain’t seen nothing yet: By packing an exceptionally high-field magnet into a coil you could pack in a purse, MagLab scientists and engineers have shown a way to build and use electromagnets that are stronger, smaller and more versatile than ever before.
Their work is outlined in an article published today in the journal Nature.
“We are really opening a new door,” said MagLab engineer Seungyong Hahn, the mastermind behind the new magnet and an associate professor at the FAMU-FSU College of Engineering. “This technology has a very good potential to entirely change the horizons of high-field applications because of its compact nature.”
Both the 45-T magnet and the 45.5-T test magnet are built in part with superconductors, a class of conductors boasting special properties, including the ability to carry electricity with perfect efficiency.
The superconductors used in the 45-T are niobium-based alloys, which have been around for decades. But in the 45.5-T proof-of-principle magnet, Hahn’s team used a newer compound called REBCO (rare earth barium copper oxide) with many advantages over conventional superconductors.
Notably, REBCO can carry more than twice as much current as a same-sized section of niobium-based superconductor. This current density is crucial: After all, the electricity running through an electromagnet generates its field, so the more you can cram in, the stronger the field.
Also critical was the specific REBCO product used—paper-thin, tape-shaped wires manufactured by SuperPower Inc.
MagLab Chief Materials Scientist David Larbalestier, who is also a professor at the FAMU-FSU College of Engineering, saw the product’s promise to pack more power into a potential world-record magnet, and encouraged Hahn to give it a go.
The other key ingredient was not something they put in, but rather something they left out: insulation.
Today’s electromagnets contain insulation between conducting layers, which directs the current along the most efficient path. But it also adds weight and bulk.
Hahn’s innovation: A superconducting magnet without insulation. In addition to yielding a sleeker instrument, this design protects the magnet from a malfunction known as a quench. Quenches can occur when damage or imperfections in the conductor block the current from its designated path, causing the material to heat up and lose its superconducting properties. But if there is no insulation, that current simply follows a different path, averting a quench.
“The fact that the turns of the coil are not insulated from each other means that they can share current very easily and effectively in order to bypass any of these obstacles,” explained Larbalestier, corresponding author on the Nature paper.
There’s another slimming aspect of Hahn’s design that relates to quenches: Superconducting wires and tapes must incorporate some copper to help dissipate heat from potential hot spots. His “no-insulation” coil, featuring tapes a mere 0.043-mm thick, requires much less copper than do conventional magnets.