Hybrid magnet in China produces record-breaking steady field of 45.22 T

Scientists of the Steady High Magnetic Field Facility in Hefei built it.

The graph shows the magnetic field strength contributions and record. | Photo Credit: SHMFF

ON August 12, the hybrid magnet built by scientists of the Steady High Magnetic Field Facility (SHMFF) in Hefei, China, produced a steady field of 45.22 tesla (T), which is a world record for the highest steady magnetic field strength by an operational working magnet. The highest field strength achieved before this was 45 T in 1999, also with a hybrid magnet, at the National High Magnetic Field Laboratory (MagLab) in Florida, US. (The earth’s magnetic field is about 35 microtesla; the strength of a refrigerator magnet is a few millitesla; pulsed magnetic fields can be orders of magnitude greater than the steady field achieved in laboratories).

MagLab and SHMFF employed different ways of creating a magnetic field in combination, hence hybrid: an outer superconducting ring and an inner resistive Bitter electromagnet. Bitter magnets, invented in 1933 and used to achieve very high magnetic fields, are made of circular conducting metal plates and insulating spacers stacked in a helical configuration. The record-breaking 45.22 T hybrid magnet is composed of a resistive insert nested in a superconducting outer ring with a bore of 32 mm.

Both technologies have their limitations. While the superconducting magnet has low power input needs but an upper limit on magnetic field strength, the Bitter magnet requires a much higher power input. Combining the two mitigates these limitations significantly and enables propagation of a powerful, steady magnetic field. 

In 2016, the Chinese team succeeded in fabricating a hybrid magnet that generated a central magnetic field of 40 T, which at the time made it the second strongest field strength achieved in the world. “To achieve higher magnetic field, we innovated the structure of the magnet and developed new materials,” Professor Kuang Guangli, the academic director of High Magnetic Field Laboratory of the Hefei Institutes of Physical Science, said in a statement. “The manufacturing process of the Bitter discs was also optimised,” he added.