China has built and tested the largest superconducting magnet ever made for a nuclear fusion reactor, a step towards its goal of turning the technology into a working energy source.
The 582-tonne toroidal-field coil passed full-load testing on 27 June at the Institute of Plasma Physics under the Chinese Academy of Sciences in Hefei, eastern China.
It was made for the Comprehensive Research Facility for Fusion Technology, a project known as an artificial sun because it aims to recreate the reaction that powers the real one.
The D-shaped coil measures 21 metres long, 12 metres wide and 3.3 metres high, heavier than a fully loaded Boeing 747.
It holds 1.3 times the volume and three times the stored energy of the equivalent magnet built for the International Thermonuclear Experimental Reactor, the 35-nation project under construction in southern France.
Caging the plasma
The magnet's job is containment. A fusion reactor heats plasma, an electrically charged gas, to more than 100 million degrees Celsius, far hotter than the roughly 15 million degrees at the sun's core.
No physical wall can touch matter that hot, so the coil generates a magnetic field that holds the plasma in a doughnut-shaped chamber, away from the vessel walls.
The device tested in June is one of 16 identical coils intended to form the full magnetic cage, each carrying 100 kiloamperes and producing 6.5 tesla at the centre, more than four times the field of a hospital MRI scanner.
A high-temperature superconducting central solenoid, which starts and drives the plasma current, was tested alongside it.
Built at home
The point Chinese officials stressed was self-reliance.
According to the state news agency Xinhua, every critical technology in the programme was developed domestically, from the superconducting wire to the cryogenic steel that carries the load.
Song Yuntao, the institute's director, said the coil took six years to build and had the highest energy-storage capacity of its type in the world.
The magnet must operate for a designed service life of 60 years under extreme conditions: ultra-low temperatures, high currents, intense radiation and heavy mechanical stress.
The coil is destined for BEST, the Burning Plasma Experimental Superconducting Tokamak, a compact fusion device under construction in Hefei and targeted for completion around 2027.
The wider race
The achievement clears one engineering hurdle, not the whole course.
An institute researcher told the Global Times that the tests represented about 80% of the task, with assembly of the full device still ahead, and commercial fusion power remains years away.
The move fits a familiar Chinese pattern, mirroring its rise in solar panels and electric vehicles, this time aimed at the energy source that could underpin power-hungry AI data centres.
Western efforts lean more on private capital, with companies such as Commonwealth Fusion Systems raising billions and targeting commercial operation by 2027.
Much of the detailed performance data comes from Chinese institute releases and state media, so independent verification will matter as the project moves from component testing to a working reactor.
