By the late 1970s, it was clear that the next major step towards a fusion power plant would require a very large and technically demanding experimental device. The scientific, engineering and financial challenges were difficult for any single country to tackle alone, making international cooperation increasingly attractive.

INTOR

The first major international effort of this kind began in 1978 under the auspices of the IAEA. The INTOR project (International Tokamak Reactor) brought together experts from the Soviet Union, Euratom, the United States and Japan to assess the scientific and technological basis for a next-step tokamak reactor. A conceptual design was completed in 1981 and updated in 1983 and 1985, while the collaboration continued until 1987. Although INTOR was never built, it demonstrated that sustained international cooperation on a large fusion project was possible and provided an important foundation for ITER. At the time, however, there was not yet sufficient political commitment to proceed with construction of such a large international facility.

International Thermonuclear Experimental Reactor

US President Reagan and Soviet General Secretary Gorbachev during the Geneva Summit, 1985.

A decisive political step came at the Geneva Superpower Summit in November 1985, when Soviet General Secretary Mikhail Gorbachev proposed to US President Ronald Reagan an international effort to develop fusion energy for peaceful purposes. In 1986, Euratom, Japan, the Soviet Union and the United States agreed to pursue jointly the design of a large international fusion facility. The project was originally named the International Thermonuclear Experimental Reactor, giving rise to the acronym ITER. The name was later retained primarily for its Latin meaning, “the way”, symbolising a path towards practical fusion energy.

Negotiations

Conceptual design work on ITER began in 1988, followed by Engineering Design Activities from 1992. A first Final Design Report was approved in 1998, but in the same year the United States withdrew from the project because of concerns about cost. The remaining partners subsequently developed a smaller and less expensive design, which was approved in 2001 and forms the basis of the present ITER machine.

Negotiations then turned to the future ITER site. Canada, although not an ITER Member, proposed a site at Clarington, Ontario, in 2001. Europe later nominated Cadarache in southern France, while Japan proposed Rokkasho-Mura. The Canadian proposal was eventually withdrawn, leaving the European and Japanese sites as the final candidates.

In 2003, China and the Republic of Korea joined the project, and the United States rejoined. The site-selection process eventually narrowed the choice to Cadarache in France and Rokkasho-Mura in Japan. India joined ITER in 2005, bringing the number of Members to seven.

Both candidate sites had advantages and disadvantages. Cadarache was located inland, about 106 km from the nearest suitable harbour, which complicated the transport of very large components. Rokkasho-Mura offered strong industrial and port infrastructure but also required careful consideration of seismic conditions. Neither Europe nor Japan was initially willing to withdraw its candidacy, and the site-selection negotiations remained deadlocked for several years.

Broader Approach

To resolve the site-selection deadlock, Europe and Japan developed the Broader Approach, a complementary fusion-research partnership that would provide major research facilities and programmes in Japan while ITER itself was hosted in Europe. The arrangement was designed to ensure that both sides gained substantial scientific and technological benefits from the agreement.

On 28 June 2005, the ITER Members unanimously selected Cadarache as the construction site. The ITER Agreement was signed in Paris on 21 November 2006 by China, the European Union, India, Japan, Korea, Russia and the United States, and the ITER Organization was formally established on 24 October 2007 after ratification by all seven Members.

The collaboration is based largely on in-kind contributions: around 90 percent of the project’s construction value is supplied by the Members in the form of completed components, systems and buildings. Major components are manufactured across the seven Members and transported to Cadarache, where they are integrated into a single machine with extremely tight tolerances. ITER is still under construction and assembly. Under the current baseline, Start of Research Operation is planned for 2034, full magnetic energy for 2036 and the beginning of deuterium–tritium operation for 2039.

Idea of DEMO

ITER is intended to provide the scientific and technological basis for the next generation of fusion devices commonly referred to as DEMO — demonstration fusion power plants designed to produce electricity and test technologies required for commercial operation.

Today, several ITER Members are pursuing their own DEMO concepts and development pathways rather than a single common machine. Europe aims for a demonstration power plant around 2050, while Japan, Korea and other Members are developing their own concepts with differing mid-century or later schedules. The exact designs and timelines remain under development.