India has become the latest nation to join the global project building a prototype nuclear fusion reactor.
It joins China, the EU, Japan, South Korea, Russia and the US in the International Thermonuclear Experimental Reactor (Iter) team.
At a meeting on the Korean island of Jeju, Iter also named a new director-general, Kaname Ikeda.
The 10bn euro (£6.7bn) Iter project is designed to produce electricity using nuclear fusion, as happens in the Sun.
It will be built at Cadarache in France; construction will take at least a decade.
An Iter statement on India's accession comments: "With this exciting new development, over half the world's population is now represented in this global endeavour."
Iter will be the second largest science project in history after the International Space Station.
After decades of experimentation at national and regional level, it should demonstrate once and for all whether it is possible to harness the tremendous potential of nuclear fusion in a practical and economic way.
ITER - NUCLEAR FUSION PROJECT
Project estimated to cost 10bn euros and will run for 35 years
It will produce the first sustained fusion reactions
Final stage before full prototype of commercial reactor is built
Fusion works by forcing together atomic nuclei, rather than by splitting them as in the case of the fission reactions that power existing nuclear stations.
In the core of the Sun, huge gravitational pressures allow this to happen at around 10 million degrees Celsius. These pressures cannot be created on Earth, so temperatures need to be much higher - above 100 million degrees Celsius.
No materials could withstand direct contact with such heat; the favoured solution is to hold a super-heated gas, or plasma, of hydrogen fuel inside an intense doughnut-shaped magnetic field.
Unlike the burning of fossil fuels, fusion reactions produce no carbon dioxide and so the process contributes almost nothing to the greenhouse effect.
It is also inherently powerful, and could potentially provide a solution to the energy shortages coming over the course of this century.
But the huge technical issues involved prompt sceptics to suggest it may never work.
India's involvement in the project, which has been welcomed by the European Commission and the US administration, suggests that it is among the optimists.