The engineers and scientists at the National High Magnetic Field Laboratory [NHMFL] in Florida, announced this week that they had successfully tested a new resistive electromagnet that produces a magnetic field strength of 36 tesla (360 kilo-oersted), breaking the old record of 35 tesla (350 kilo-oersted) previously held jointly between the NHMFL and the Grenoble High Magnetic Field Laboratory in France.
The device is actually an upgrade to an existing electromagnet, and uses a special coil design called a Bitter solenoid, in order to generate the intense magnetic field. This design, first invented by Prof. Francis Bitter while working at MIT prior to World War Two, consists of stacks of copper plates, instead of wire coils, in order to carry the massive currents that are required for the electromagnet. The working inner bore of the new magnet is approximately 32 mm [1.25 inches] in diameter.
The increment from 35 T to 36 T came from creating a new arrangement of the copper plates in the Bitter solenoid. The researchers at the NHMFL plan to apply this new arrangement and upgrade the rest of the electromagnets at the lab, in order to increase the overall magnetic output of each. As an added bonus, according to laboratory:
[t]his cost-neutral modification means a higher magnetic field can be created using the same amount of power, 20 megawatts. By comparison, the magnet at the Grenoble High Magnetic Field Laboratory achieves its 35 tesla using 22.5 megawatts of power.
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To put this into context, 20 megawatts of electricity is enough electricity to power around 6,000-7,000 average American homes. A 2.5 MW saving in electricity [equivalent to the power produced by a commercial scale wind turbine these days], for the same magnetic output, is therefore pretty significant. During a visit to the NHMFL a few years ago, I was told that the laboratory is required to give plenty of notice to the local municipality in Tallahassee before switching on their electromagnets, because of the massive current draw on the local grid that they cause.
It was in a very high field electromagnet of this type, that the famous picture of the floating frog shown here, was taken some years ago. The strong diamagnetic effect of the electromagnet, on the water molecules in the frog’s body, is enough to counter the effects of gravity. When not levitating amphibians and other objects, researchers use these types of very strong electromagnets for physics and materials science research.