Even small magnets can sometimes be exceptionally powerful
ResonX /Jasmin Schoenzart
A magnet small enough to fit in the palm of your hand can match the strength of some of the world’s most powerful magnets for the first time.
Strong magnets play many roles across science and technology, with uses in everything from MRI imaging and particle accelerators to nuclear fusion efforts. The most powerful among them are made of superconductors, materials that conduct electricity with almost perfect efficiency.
But superconducting magnets that produce strong magnetic fields are often bulky: smaller magnets are usually the same size as Star Wars robot R2D2, while the largest ones are comparable to a two-storey building, says Alexander Barnes at ETH Zurich in Switzerland.
He and his colleagues have now built a superconducting magnet that is competitive with the large magnets in strength, but measures just 3.1 millimeters in diameter. They made it by coiling a thin tape of a ceramic material called REBCO, which superconducts when cooled to extremely low temperatures. These coils produce magnetic fields when electric currents are passed through them.
The team purchased the REBCO tape from a commercial company, then set out to find the best magnet design, which involved making and testing over 150 of them, Barnes says. “Our strategy was to develop and embrace a ‘fail often and fail fast’ approach.”
They finally settled on a design involving either two or four pancake-shaped coils of REBCO that could produce magnetic fields with strengths of 38 Tesla and 42 Tesla, respectively. By comparison, a refrigerator magnet typically has a magnetic field strength below 0.01 Tesla. The two magnets which today produce the world’s strongest steady magnetic field reaching around 45 Tesla, weigh many tonnes and require up to 30 megawatts of power. Barnes and team’s magnet is smaller than your hand and requires less than 1 watt of power.
Barnes says their ultimate goal is to use this magnet for nuclear magnetic resonance (NMR), an experimental technique that uses magnetic fields to reveal the structure of molecules such as drugs and catalysts for industrial processes. In his view, this powerful technique is hindered by the size and cost of magnets, but the researchers hope to make it available to more chemists. The team has already started testing the magnet in an NMR setup, says Barnes.
“Producing magnetic fields above 40 Tesla traditionally requires very large and expensive facilities, so it is important to achieve similar field strengths in such a compact device using superconducting ribbons,” says Mark Ainslie of King’s College London. “It suggests that extremely high-field magnets may become more accessible to a wider range of laboratories in the near future.”
But questions remain before the magnet can achieve widespread use – for example, how uniform the magnetic field can be made and how the electromagnetic behavior of these coils can be directed and controlled, he says.
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