Fusion Reactor

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Lore & Background

ITER (originally an acronym for International Thermonuclear Experimental Reactor, and also meaning 'the way' or 'the path' in Latin) is an international nuclear fusion research and engineering project. The initial international cooperation began in 1978 with the International Tokamak Reactor, or INTOR, which had four partners: the Soviet Union, the European Atomic Energy Community, the United States, and Japan. The INTOR project stalled until Mikhail Gorbachev revived interest in a collaborative fusion project in an October 1985 meeting with French President François Mitterrand, and the idea was further developed in November 1985 at the Geneva Summit with Ronald Reagan. On 21 November 2006, the seven project partners formally agreed to fund the creation of a nuclear fusion reactor. ITER is funded and operated by seven member parties: China, the European Union (EU), India, Japan, Russia, South Korea and the United States. In the immediate aftermath of Brexit, the United Kingdom continued to participate through the EU's Fusion for Energy (F4E) program until September 2023. Switzerland participated through Euratom and F4E until 2021, though it is poised to rejoin in 2026 following subsequent negotiations with the EU. ITER also has cooperation agreements with Australia, Canada, Kazakhstan and Thailand. Construction of the ITER complex in France started in 2013, and assembly of the tokamak began in 2020. The initial budget was close to €6 billion, but the total price of construction and operations is projected to be from €18 to €22 billion; other estimates place the total cost between $45 billion and $65 billion, though these figures are disputed by ITER. Regardless of the final cost, ITER has already been described as the most expensive science experiment of all time, the most complicated engineering project in human history, and one of the most ambitious human collaborations since the development of the International Space Station and the Large Hadron Collider.

In Their Own Story

ITER's goals include to achieve fusion energy gain factors (Q, the ratio of thermal output power as thermal power absorbed by the plasma) of Q = 10 momentarily and Q = 5 at steady state; to develop fusion power technologies including superconducting magnets, cryogenics, heating, control and diagnostics systems, and remote handling; to study burning plasma; to test tritium breeding; and to demonstrate the safety of a fusion plant. ITER will use over 300 MW of electrical power to cause the plasma to absorb 50 MW of thermal power, creating 500 MW of heat from fusion for periods of 400 to 600 seconds. This would mean a ten-fold gain of plasma heating power QDT, or QDT ≥ 10. The record value of the ratio of the fusion power produced in the core of a tokamak to the applied heating power entering the core Qcore is 1.3 in the JET Joint European Torus experiment calculated using the TRANSP code. As of 2022, the record for energy production using nuclear fusion is held by the National Ignition Facility reactor, which achieved a Qcore of 1.5 in December 2022. Beyond just heating the plasma, the total electricity consumed by the reactor and facilities will range from 110 MW up to 620 MW peak for 30-second periods during plasma operation. As a research reactor, the heat energy generated will not be converted to electricity, but simply vented. ITER's planned successor, the EUROfusion-led DEMO, is expected to be one of the first fusion reactors to produce electricity in an experimental environment.

Reader's Guide

One of the primary ITER objectives is to achieve a state of 'burning plasma'. Burning plasma is the state of the plasma when more than 50% of the energy received for plasma heating is received from fusion reactions (not from external sources). No fusion reactors had created a burning plasma until the competing NIF fusion project reached the milestone on 8 August 2021 using inertial confinement. At higher QDT values, progressively bigger parts of plasma heating power will be produced by fusion reactions. This reduces the power needed from external heating systems at high QDT values. The bigger a tokamak is, the more fusion-reaction-produced energy is preserved for internal plasma heating (and the less external heating is required), which also improves its Q-value. This is how ITER plans for its tokamak reactor to scale. ITER will not produce electricity. Producing electricity from thermal sources is a well-known process and ITER will not run with significant fusion power output continuously. Adding electricity production to ITER would raise the cost of the project and bring no value for experiments on the tokamak. The DEMO-class reactors that are planned to follow ITER are intended to demonstrate the net production of electricity.

Did You Know?

• ITER is an acronym for International Thermonuclear Experimental Reactor, and also means 'the way' or 'the path' in Latin.
• The initial budget was close to €6 billion, but the total price of construction and operations is projected to be from €18 to €22 billion.
• ITER's planned successor, the EUROfusion-led DEMO, is expected to be one of the first fusion reactors to produce electricity in an experimental environment.
• The best result achieved in a tokamak is Q = 0.67 in the JET tokamak.
• The best result achieved for fusion in general is Q = 4.13, achieved in an inertial confinement fusion experiment by the National Ignition Facility in April 2025.