FAQs

ITER (the Latin word for "The Way") is a large-scale scientific experiment intended to prove the viability of fusion as an energy source. ITER is currently under construction in the south of France. In an unprecedented international effort, seven partners—China, the European Union, India, Japan, Korea, Russia and the United States—have pooled their financial and scientific resources to build the biggest fusion reactor in history. ITER will not produce electricity, but it will resolve critical scientific and technical issues in order to take fusion to the point where industrial applications can be designed. By producing 500 MW of fusion power from 50 MW of power injected in the systems that heat the plasma—a "gain factor" of 10—ITER will open the way to the next step: a demonstration fusion power plant.

On-site construction of the scientific facility began in 2010. As the buildings rise at the ITER site in southern France, the fabrication of large-scale mockups and components is underway in the factories of the seven ITER Members. Component deliveries are accelerating and in May 2020, the first "piece" of the machine—the 1,250-tonne cryostat base—was introduced into the completed tokamak pit. 

ITER is one of the most complex scientific and engineering projects in the world today. The complexity of the ITER design has already pushed a whole range of leading-edge technologies to new levels of performance. However, further science and technology are needed to bridge the gap to the commercialization of fusion energy.

ITER is the experimental step between today's fusion machines, focused on plasma physics studies, and tomorrow's fusion power plants.

The plasma physics community will have access for the first time, in ITER, to a burning plasma. In a burning plasma, the energy of the helium nuclei produced by the fusion reactions is enough to maintain the temperature of the plasma, thereby reducing or eliminating the need for external heating. Self-heating plasmas will be the key in the future to producing electricity from fusion energy, allowing for sustained, ongoing fusion reactions.

To be able to create plasmas with dominant self-heating, ITER will be twice as large as the largest tokamak fusion experiment currently operating, JT-60SA (Europe/Japan), with six times the plasma volume. This unique experimental machine has been designed to:

• Confine a deuterium-tritium plasma in which alpha-particle heating (self-heating) dominates
• Generate 500 MW of fusion power in its plasma from 50 MW of heating input power (Q≥10) for long durations (400 to 600 seconds)
• Contribute to the demonstration of the integrated operation of technologies for a fusion power plant
• Test concepts for a tritium breeding module
• Demonstrate the safety characteristics of a fusion device
• Fusion is a promising option long-term for sustainable, global energy supply if the remaining technical challenges can be overcome.

In a project of this unprecedented scale, involving worldwide cooperation and billions of euros of expenditure, it would be naïve to believe that there could be unanimity in the scientific community on the aims and the scientific and technical basis of the project. A scientific consensus may be possible while discussions remain at the abstract level, but in a world of intense competition for research funding it is inevitable that scientists from various fields will criticize the decision to spend money on a large project, arguing that they would prefer to spend the money elsewhere.

What can be said about ITER is that for the scientific community working in the energy field, this project is considered by a strong majority as a major step toward providing a future energy alternative for all humankind. The present political and scientific approach to this project has not suddenly appeared out of lobbying by a few influential individuals. It is the result of decades of painstaking, step-by-step research by fusion scientists all over the world as well as intense discussions in the scientific administrations of involved governments who debated the options, the costs and the risks before deciding that ITER was a worthwhile investment in our common energy future. The proportion of papers directly concerned with ITER presented at leading international scientific conferences on fusion as well as in fusion journals has been steadily increasing for a number of years. The fact that research aimed at ITER is now such a dominant topic in these papers demonstrates how essential the project is to the advancement of fusion towards energy production.

While ITER's future operation as a burning plasma device is clearly the core of ITER's mission and the most anticipated outcome of the project, it is also important to point out the benefits realized so far during the design, construction, manufacturing and installation/assembly phases. Hundreds of engineering challenges associated with ITER's many first-of-a-kind components have already been overcome, demanding innovation and engineering breakthroughs from some of the top laboratories and companies globally. In that sense, the global ITER project is already a learning laboratory. Anecdotally, many within the global fusion R&D community report that the surge in private sector fusion projects, and the associated investment, has been driven by ITER's success in these early phases.

Fusion research, and the role of ITER, has been subject to serious scrutiny by panels of independent experts established by funding agencies in Europe and most of the other ITER partners. The results of these investigations provide the most reliable measure of consensus in the scientific community. A few examples:

• In 2004 during the early stages of ITER negotiations, a high-level panel chaired by Sir David King (Chief Scientific Advisor to the UK government) concluded that the time was right to press ahead with ITER and recommended funding a "fast track" approach to fusion energy. In 2013 the European Fusion Development Agreement (EFDA, now EUROfusion) published The European Research Roadmap to the Realisation of Fusion Energy by 2050. The roadmap was updated in 2018.
• The French Academy of Sciences organized a detailed review of the state-of-the-art and the remaining challenges of fusion both by magnetic confinement (including ITER) and using laser-driven systems. The review was published in a book in 2007 which emphasized the arguments supporting the construction of ITER.
• The United States went through a long process to decide to re-enter the ITER collaboration, after leaving it in the late 1990s. The US National Academy of Sciences convened a panel which included both fusion scientists and senior scientists from related fields such as nuclear fission power, high-energy physics and astrophysics. The non-fusion scientists were empowered to make the key recommendations. The panel strongly endorsed the renewed membership of the US in the ITER project as the best path forward to fusion energy.
• China announced in 2011 that it is planning to train 2,000 skilled experts over 10 years to carry out research and development in fusion.
• In May 2016, the US Department of Energy made a report to the US Congress in which it recommends that the US remain a partner in ITER, through a re-assessment in 2018. Noting that "the management of the ITER Organization and the performance of the project have improved substantially," the report concludes that despite accumulated delays, "ITER remains the fastest path for the study of burning plasma."
• In June 2017 the European Commission produced the 14-page document "EU Contribution to a Reformed ITER Project" expressing confidence that the project was back on track.
• In December 2017, the US National Academy of Sciences issued the first part of a two-phase study on the state and potential of magnetic fusion research in the US. In it, US policy makers were urged to continue to participate in the ITER project and to develop a long-term strategy for fusion energy demonstration. (The report is available here.)
• In April 2018 the European Council of Ministers issued a statement mandating Commission to approve the new ITER Baseline (cost, schedule, scope). One month later, the European Commission issued its 2021-2017 budget proposal with unequivocal support for the ITER project.
• In 2019 the US National Academy of Sciences published its final report (available here), recommending not only that the US remain a partner in ITER "as the most cost-effective way to gain experience with a burning plasma at the scale of a power plant," but also that it start a "national program of accompanying research and technology leading to the construction of a compact pilot plant."
• In March 2020, hundreds of scientists across the United States—representing a broad range of national labs, universities, and private ventures—released A Community Plan for Fusion Energy and Discovery Plasma Sciences. It offers a consensus view of the bold steps to take nationally to deliver fusion energy and advance plasma science in the United States, including maintaining participation in ITER. (Download the report here.) The recommendations served as a basis for the final US Department of Energy, Fusion Energy Sciences Advisory Committee (FESAC) report Powering the Future: Fusion & Plasmas, which was adopted in December 2020 and will now serve as advisory input to the DOE Office of Fusion Energy Sciences, which is responsible for all decisions and implementation.
• At the request of the US Department of Energy (DOE), a committee of 12 scientists has written Bringing Fusion to the U.S. Grid, with the aim of providing guidance on the key goals and innovation needed to build an electricity-producing fusion power plant at lowest possible capital cost. The report, released in February 2021, calls for the construction of a 50-megawatt pilot fusion power plant. Download the full report here. In December 2023, the DOE released Building Bridges: A Vision for the Office of Fusion Energy Sciences. In June 2026, the DOE released the final version of its Fusion Science and Technology Roadmap, a national strategy to accelerate the development and commercialization of fusion energy.
• The United Kingdom first set out a detailed strategy for fusion in 2021 and updated its strategy in 2026 (see the UKAEA Fusion Roadmap 2026-2030 here). The document is based on a two-pronged approach: building a prototype fusion power plant in the UK that delivers net energy (STEP), and building up a world-leading fusion industry that supports different fusion technologies.
• Recent publications make it clear that the governments of China (and also here and here), Europe (and also here and here), Germany (and also here and here), India, Japan (here and also here), Korea (and here), and Russia are also actively pursuing long-term strategies for investment in fusion research. In early 2024, China announced the launch of a fusion consortium, Fusion Energy Inc, that aims to build an industrial prototype fusion reactor. In April 2024, Japan and the United States signed a partnership agreement to accelerate fusion energy demonstration and commercialization.
• Activity in the private sector is also accelerating, with at least 43 private fusion initiatives operating now in 12 countries, benefitting from more than USD 7 billion in private investment. (See resources below.)
• The latest independent analysis (2026) commissioned by the European Domestic Agency Fusion for Energy on the ripple effect from its investment in fusion energy activities reveals returns in knowledge, growth and jobs for the companies involved. Since its creation in 2007, F4E has invested more than EUR 7 billion to provide Europe’s contribution to ITER and other international projects through more than 1,400 contracts. This has shaped the largest supply chain in the world, with at least 2,700 companies and 75 R&D organizations. 

See these general sources of information on global fusion energy initiatives: the IAEA World Fusion Outlook 2025, the IAEA Fusion Device Information System FusDIS, the Global Fusion Industry in 2026 (Fusion Industry Association) and the 2026 Fusion Industry Supply Chain Report (Fusion Industry Association).

The first small-size tokamaks (1950s-1970s) were basic devices without sophisticated control systems and technology, but they demonstrated that high temperature plasmas could be generated and that energy could be confined. New plasma phenomena such as anomalous transport, instabilities and disruptions were uncovered during these first experiments. Scaling laws indicated that energy confinement could be increased in larger devices with higher magnetic fields.

The second-generation, medium-sized devices in the 1980s introduced the extensive use of auxiliary heating techniques. The addition of the divertor demonstrated improved confinement; wall conditioning techniques were also introduced. The ASDEX Tokamak achieved high confinement mode for the first time in 1982.

A new generation of larger tokamaks—JET (Europe), JT-60 (Japan), TFTR (US), KSTAR (Korea) and T-15 (Soviet Union)—were built to study plasmas in conditions as close as possible to those of a fusion reactor, and regularly upgraded based on advances in fusion science. New features such as superconducting coils, deuterium-tritium operation, and remote handling were introduced. The experience accumulated on these machines contributed to the design of ITER.

Today, fusion research is at the threshold of exploration of a "burning plasma" in which sufficient heat from the fusion reaction is retained within the plasma and sustains the reaction for a long duration. Such exploration is a necessary step toward the realization of a fusion energy source; it must be done to establish the confidence in proceeding with demonstrations of practical fusion energy. Construction of ITER and implementation of the ITER research program would provide for such exploration.

Tokamaks around the world are helping to prepare for the construction and operation of ITER. See more in International Tokamak Research.

Of the magnetic confinement concepts for fusion (mainly tokamaks and stellarators) the main advantage of ITER and its tokamak technology is that, for the time being, the tokamak concept is by far the most advanced along the road to producing fusion energy. It is consequently pragmatism that dictated the choice of the tokamak concept for ITER. Stellarators are inherently more complex than tokamaks (for example, optimized designs were not possible before the advent of supercomputers) but they may have advantages in reliability of operation. The Wendelstein 7-X stellarator, which celebrated its first plasma in 2015 in Greifswald, Germany, will allow good benchmarking against the performance of comparable tokamaks. These results will be incorporated in decisions about how DEMO, the next-generation fusion device after ITER, will look.

The inertial fusion concepts are something quite different. These technologies have mainly been developed to simulate nuclear explosions and were not originally planned to produce fusion energy. The inertial fusion concept has not demonstrated so far that it offers a better or shorter path than magnetic confinement to energy production. However, interesting results were obtained in late 2022 in the National Ignition Facility (United States) when, for the first time, researchers successfully used 2.05 megajoules of laser energy to produce 3.15 megajoules of fusion energy, reaching a Q value of 1.5. (See more details here.) 

It should also be noted that in the last five years, a large number of private startups have entered the ring, raising an estimated USD 6 billion to develop alternative types of fusion reactors. Each one of these is contributing in some way to a shared goal: bringing fusion electricity to the grid.

The choice was made from the beginning to share the manufacturing of the most strategically important components among the seven ITER Members. This has considerably added to the complexity of the project, but the reasons for this decision were clear—by participating in ITER, each Member is preparing its industrial infrastructure, its scientific base, and its physicists and engineers for the next step on the road to fusion power: the construction of a demonstration fusion power plant.

It seems clear that no one Member has the financial and technical resources to build ITER alone. In this sense, by contributing only a portion of the project's costs, each Member benefits from the totality of the development program (where, already, there have been discoveries in technology, materials, science and even the first applications for patents) and, later, the totality of the 20-year experimental program. 

Collaboration and coordination between the different entities of the project is improving all of the time. What is remarkable about fusion research is that, for a very long time, it has been an international, collaborative venture where discoveries in one area of the world immediately benefit other research programs. This is true every day at ITER, where the project benefits from the diverse experiences of its Members, including research underway on operational tokamaks in different parts of the world.

If ITER were only a construction project, its model would certainly have been organized differently. But as the world's largest and most challenging energy research project, the collaboration between seven ITER Members—all with decades of experience in fusion—has been most profitable in terms of pooling resources to solve the difficult challenges that remain on the road to fusion.

In withdrawing from the European Union (EU) on 31 January 2020, the United Kingdom (UK) has also withdrawn from the European Atomic Energy Community (Euratom). Like all EU Member States, the UK had participated in the ITER Project through Euratom, which is the contracting party to the ITER Agreement.

During the 11-month transition period through the end of the calendar year 2020, UK officials made clear that they wished to remain part of the ITER Project. 

On 30 December 2020, in parallel with the 1,246-page Trade and Cooperation Agreement signed by the United Kingdom and the European Union, a Nuclear Cooperation Agreement (NCA) was signed between the UK and Euratom (the European Atomic Energy Community), the legal entity through which Europe holds its membership in ITER, that made clear the intent for the UK to remain a part of Fusion for Energy, the European Domestic Agency for ITER. 

Negotiations came to an end in September 2023 when the United Kingdom announced that it would no longer pursue an association with Euratom, deciding instead "to pursue a domestic fusion energy strategy." The strategy includes the ambition to develop "close international collaboration," including with ITER. Until the terms of possible association with ITER are established, the ITER Project is in general no longer hiring UK citizens or contracting with UK companies; ITER is however continuing to honour existing contracts.