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ITER completes world's largest and most powerful pulsed magnet system

In a landmark achievement for fusion energy, ITER has completed all components for the world's largest, most powerful pulsed superconducting electromagnet system.

ITER is an international collaboration of more than 30 countries to demonstrate the viability of fusion—the power of the sun and stars—as an abundant, safe, carbon-free energy source for the planet.

The final component was the sixth module of the Central Solenoid, built and tested in the United States. When it is assembled at the ITER site in Southern France, the Central Solenoid will be the system's most powerful magnet, strong enough to lift an aircraft carrier.

The Central Solenoid will work in tandem with six ring-shaped Poloidal Field (PF) magnets, built and delivered by Russia, Europe, and China.

The fully assembled pulsed magnet system will weigh nearly 3,000 tons. It will function as the electromagnetic heart of ITER's donut-shaped reactor, called a Tokamak.

How does this pulsed superconducting electromagnet system work?

Step 1. A few grams of hydrogen fuel—deuterium and tritium gas—are injected into ITER's gigantic Tokamak chamber.

Step 2. The pulsed magnet system sends an electrical current to ionize the hydrogen gas, creating a plasma, a cloud of charged particles.

Step 3. The magnets create an "invisible cage" that confines and shapes the ionized plasma.

Step 4. External heating systems raise the plasma temperature to 150 million degrees Celsius, ten times hotter than the core of the sun.

Step 5. At this temperature, the atomic nuclei of plasma particles combine and fuse, releasing massive heat energy.

A 10-fold energy gain

At full operation, ITER is expected to produce 500 megawatts of fusion power from only 50 megawatts of input heating power, a tenfold gain. At this level of efficiency, the fusion reaction largely self-heats, becoming a "burning plasma."

By integrating all the systems needed for fusion at an industrial scale, ITER is serving as a massive, complex research laboratory for its 30-plus member countries, providing the knowledge and data needed to optimize commercial fusion power.

A global model

ITER's geopolitical achievement is also remarkable: the sustained collaboration of ITER's seven members—China, Europe, India, Japan, Korea, Russia, and the United States. Thousands of scientists and engineers have contributed components from hundreds of factories on three continents to build a single machine.

Pietro Barabaschi, ITER Director-General, says, "What makes ITER unique is not only its technical complexity but the framework of international cooperation that has sustained it through changing political landscapes."

"This achievement proves that when humanity faces existential challenges like climate change and energy security, we can overcome national differences to advance solutions."

"The ITER Project is the embodiment of hope. With ITER, we show that a sustainable energy future and a peaceful path forward are possible."

In 2024, ITER reached 100% of its construction targets. With most of the major components delivered, the ITER Tokamak is now in assembly phase. In April 2025, the first vacuum vessel sector module was inserted into the Tokamak Pit, about 3 weeks ahead of schedule.

Extending collaboration to the private sector

The past five years have witnessed a surge in private sector investment in fusion energy R&D. In November 2023, the ITER Council recognized the value and opportunity represented by this trend.

They encouraged the ITER Organization and its Domestic Agencies to actively engage with the private sector, to transfer ITER's accumulated knowledge to accelerate progress toward making fusion a reality.

In 2024, ITER launched a private sector fusion engagement project, with multiple channels for sharing knowledge, documentation, data, and expertise, as well as collaboration on R&D. This tech transfer initiative includes sharing information on ITER's global fusion supply chain, another way to return value to Member governments and their companies.

In April 2025, ITER hosted a public-private workshop to collaborate on the best technological innovation to solve fusion's remaining challenges.

How have ITER's members contributed to this achievement?

Under the ITER Agreement, members contribute most of the cost of building ITER in the form of building and supplying components. This arrangement means that financing from each member goes primarily to their own companies, to manufacture ITER's challenging technology. In doing so, these companies also drive innovation and gain expertise, creating a global fusion supply chain.

Europe, as the Host Member, contributes 45% of the cost of the ITER Tokamak and its support systems. China, India, Japan, Korea, Russia, and the United States each contribute 9%, but all members get access to 100% of the intellectual property.

The United States has built the Central Solenoid, made of six modules, plus a spare.

• The U.S. has also delivered to ITER the "exoskeleton" support structure that will enable the Central Solenoid to withstand the extreme forces it will generate. The exoskeleton is comprised of more than 9,000 individual parts, manufactured by eight U.S. suppliers.
• Additionally, the U.S. has fabricated about 8% of the Niobium-Tin (Nb₃Sn) superconductors used in ITER's Toroidal Field magnets.

Russia has delivered the 9-meter-diameter ring-shaped Poloidal Field magnet that will crown the top of the ITER Tokamak.

• Working closely with Europe, Russia has also produced approximately 120 tons of Niobium-Titanium (NbTi) superconductors, comprising about 40% of the total required for ITER's Poloidal Field magnets.
• Additionally, Russia has produced about 20% of the Niobium-Tin (Nb₃Sn) superconductors for ITER's Toroidal Field magnets.
• And Russia has manufactured the giant busbars that will deliver power to the magnets at the required voltage and amperage, as well as the upper port plugs for ITER's vacuum vessel sectors.

Europe has manufactured four of the ring-shaped Poloidal Field magnets onsite in France, ranging from 17 to 24 meters in diameter.

• Europe has worked closely with Russia to manufacture the Niobium-Titanium (NbTi) superconductors used in PF magnets 1 and 6.
• Europe has also delivered 10 of ITER's Toroidal Field magnets and has produced a substantial portion of the Niobium-Tin (Nb₃Sn) superconductors used in these TF magnets.
• And Europe is creating five of the nine sectors of the Tokamak vacuum vessel, the donut-shaped chamber where fusion will take place.

China, under an arrangement with Europe, has manufactured a 10-meter Poloidal Field magnet. It has already been installed at the bottom of the partially assembled ITER Tokamak.

• China has also contributed the Niobium-Titanium (NbTi) superconductors for PF magnets 2, 3, 4, and 5, about 65% of the PF magnet total—plus about 8% of the Toroidal Field magnet superconductors.
• Additionally, China is contributing 18 superconducting Correction Coil magnets, positioned around the Tokamak to fine-tune the plasma reactions.
• China has delivered the 31 magnet feeders, the multi-lane thruways that will deliver the electricity to power ITER's electromagnets as well as the liquid helium to cool the magnets to -269°C, the temperature needed for superconductivity.

Japan has produced and sent to the United States the 43 kilometers of Niobium-Tin (Nb₃Sn) superconductor strand that was used to create the Central Solenoid modules.

• Japan has also produced 8 of the 18 Toroidal Field (TF) magnets, plus a spare—as well as all the casing structures for the TF magnets.
• Japan also produced 25% of the Niobium-Tin (Nb₃Sn) superconductors that went into the Toroidal Field magnets.

Korea has produced the tooling used to pre-assemble ITER's largest components, enabling ITER to fit the Toroidal Field coils and thermal shields to the vacuum vessel sectors with millimetric precision.

• Korea has also manufactured 20% of the Niobium-Tin (Nb₃Sn) superconductors for the Toroidal Field magnets.
• Additionally, Korea has manufactured the thermal shields that provide a physical barrier between the ultra-hot fusion plasma and the ultra-cold magnets.
• And Korea has delivered four of the nine sectors of the Tokamak vacuum vessel.

India has fabricated the ITER Cryostat, the 30-meter-high, 30-meter-diameter thermos that houses the entire ITER Tokamak.

• India has also provided the cryolines that distribute the liquid helium to cool ITER's magnets.
• Additionally, India has been responsible for delivering ITER's cooling water system, the in-wall shielding of the Tokamak, and multiple parts of the external plasma heating systems.

In total, ITER's magnet systems will comprise 10,000 tons of superconducting magnets, with a combined stored magnetic energy of 51 gigajoules. The raw material to fabricate these magnets consisted of more than 100,000 kilometers of superconducting strand, fabricated in nine factories in six countries.

Technical specifications for each ITER magnet system

Central solenoid (cylindrical magnet)

• Height: 18 meters (59 feet)
• Diameter: 4.25 meters (14 feet)
• Weight: ~1,000 tons
• Magnetic field strength: 13 Tesla (280,000 times stronger than Earth's magnetic field)
• Stored magnetic energy: 6.4 Gigajoules
• Will initiate and sustain a plasma current of 15 MA for 300–500 second pulses
• Fabricated in the United States
• Material: Niobium-tin (Nb₃Sn) superconducting strand produced in Japan
• Cooling: operated at 4.5 Kelvin (-269°C) using liquid helium cryogenics to maintain superconductivity
• Structure (exoskeleton): built to withstand 100 MN (meganewtons) of force—equivalent to twice the thrust of a space shuttle launch.

Poloidal field magnets (ring-shaped magnets)

• Diameters: varying in range from 9 meters (PF1) to 10 meters (PF6) to 17 meters (PF2, PF5) to 25 meters (PF3, PF4)
• Weight: from 160 to 400 tons
• Fabricated in Russia, Europe (France) and China
• Material: niobium-titanium (NbTi) superconducting strand produced in Europe, China, and Russia
• Cooling: operated at 4.5 Kelvin (-269°C) using liquid helium cryogenics to maintain superconductivity

Toroidal field coils (D-shaped magnets, completed in late 2023)

• Each coil: 17 meters high × 9 meters wide
• Weight: ~360 tons each
• Fabricated in Europe (Italy) and Japan
• Material: niobium-tin (Nb₃Sn) superconducting strand produced in Europe, Korea, Russia, and the United States
• Cooling: operated at 4.5 Kelvin (-269°C) using liquid helium to maintain superconductivity

Correction coils and magnet feeders

• Correction Coils: manufactured by China; critical for fine plasma stability adjustments.
• Magnet Feeders: deliver cryogenics, electrical power, and instrumentation signals to the magnets; also produced by China.