The total magnetic energy of the magnet system used for the ITER nuclear fusion reactor reaches up to 41 gigajoules, which is 250,000 times stronger than the Earth’s magnetic field.
ITER, the world’s largest nuclear fusion experiment, is getting closer to its operational date after all the special magnets needed for constructing the reactor core have been transported to southern France, Interesting Engineering reported on July 1st. This marks the end of a two-decade design process for the reactor, with component production spanning three continents.
The ITER reactor will house the world’s largest vertically oriented magnets at its center. (Photo: ITER).
As the world seeks better ways to produce carbon-free energy, nuclear fusion offers a viable solution that can be turned on and off as needed. Recent advances in the field demonstrate that energy can be harnessed from fusion reactions. Currently, more than 30 countries are collaborating to build the International Thermonuclear Experimental Reactor (ITER) in France.
ITER’s design also employs a tokamak reactor, where hydrogen is pumped into a donut-shaped vacuum chamber and heated to create plasma, simulating conditions at the core of the Sun. At extremely high temperatures of 150 million degrees Celsius, nuclear fusion begins to occur. However, the plasma must be contained within the reactor walls by massive superconducting magnets.
The tokamak design of ITER utilizes niobium-tin and niobium-titanium as fuel for the magnets. The coils are energized electrically and then cooled to -269 degrees Celsius to transform them into superconducting magnets. ITER will deploy the magnets in three different configurations to create an invisible magnetic cage to confine the plasma. The outer ring shape is formed by 18 D-shaped magnets. A set of six magnets surrounds the tokamak horizontally, helping to control the plasma shape. Meanwhile, a solenoid coil at the center will use pulses to generate current within the plasma. The plasma current in ITER peaks at 15 million amperes, a record for tokamaks worldwide. In terms of magnetic energy, the total magnetic energy of the design is 41 gigajoules, which is 250,000 times stronger than the Earth’s magnetic field.
Each D-shaped magnet stands 17 meters tall, is nearly 9 meters wide, and weighs 360 tons. Ten magnets were produced in Europe by Fusion for Energy, while the remaining eight magnets, along with one spare, were manufactured by the National Institute for Quantum Science and Technology (QST) in Japan. The production process begins with a niobium-tin wire winding copper strands into a structure resembling a rope and placing it into a steel casing designed with a central conduit for helium to flow through. This structure is known as a conductor. Engineers require over 87,000 kilometers of niobium-tin wire to produce the conductors for 19 D-shaped magnets.
To create the D-shaped magnets, nearly 750 meters of conductor are twisted into a double helix and heated to 650 degrees Celsius. It is then placed into a D-shaped mold made of stainless steel. The conductor is insulated with glass and Kapton tape, welded with a laser to the cover plate to form a double-layer structure. This double-structure is insulated, removing air pockets and sprayed with synthetic resin to enhance durability. Seven such double structures are used to create the core of each D-shaped magnet. Finally, engineers place the assembly into a 200-ton stainless steel cage strong enough to withstand the forces generated by the movement of the plasma and the nuclear fusion process.
Once assembled, the ITER nuclear fusion reactor will produce 500 MW at maximum capacity. When connected to the power grid, the reactor will generate 200 MW of continuous electricity, enough to power 200,000 households.
