Despite the complexity and high research and development costs, scientists are convinced they can unlock the massive power of nuclear fusion within a generation.
On Monday the International Atomic Energy Agency (IAEA) and the Thermonuclear Experimental Reactor Organisation (ITER) signed a cooperation agreement at the opening of an IAEA fusion energy conference, held in Geneva.
"ITER is one of the most important scientific projects in the world," said IAEA's director general, Yuri Sokolov.
ITER, or "the way" in Latin, is an experimental reactor being built in Cadarache, southern France, which has a practical goal: to establish whether fusion, the nuclear reaction that powers the sun and the hydrogen bomb, can be tamed to generate useful power on Earth.
The idea is to fuse two atoms of hydrogen using powerful magnets to form helium. A small amount of mass is lost when the hydrogen atoms combine, in the process releasing vast quantities of energy.
Unlike nuclear fission, only low-level radioactive material, no more dangerous than hospital waste is left afterwards.
ITER, which was officially established in October 2007, will consolidate all that has been learnt over many decades of study and aims to be operational by 2018. If it works, and the technologies are proven to be practical, the international community will then build a prototype commercial reactor, dubbed DEMO in 2040. The final step would be to roll out fusion technology across the globe.
The Cadarache demonstration reactor is being jointly built by the United States, the European Union, Japan, China, India, Russia and South Korea. It will cost $5billion (SFr5.6 billion) to build, $5 billion to run for 20 years and a further $1billion to commission, half paid for by the EU.
However, project engineers now believe that construction costs will be 25-35 per cent above the original estimate, after reworking the design for Cadarache and taking account of new scientific data.
An independent expert group has been asked to review the new estimates and will report back by the end of 2008.
Value for money
But ITER is not a waste of money, replied Sokolov.
"Energy needs are so big that we have to explore all available resources," he said on Monday.
Fusion energy will help us meet the colossal energy we face in the future, said ITER's communication director, Neil Calder.
"People in China, India, Asia and Africa are going to be asking for huge amounts of energy," he told swissinfo. "Fusion is a way of producing energy that we know works. The energy released is clean, with very little waste, no CO2 and the fuels are limitless. A bath of water and a laptop battery would provide the energy needs of a European family for a lifetime."
Environmental groups such as Greenpeace have branded the ITER project "expensive, dubious and dangerous".
How quickly we get fusion energy depends on how much the world wants it, Calder added.
"If you look at the Los Alamos [atomic bomb] project, they had 100,000 people working on it with unlimited resources and they did it in three years; the same goes for the Apollo project to get a man on the moon. If the world wants fusion and is prepared to put the money into it, we'll certainly have it in 50 years," said Calder.
Switzerland has been closely involved in the ITER project, although it is not one of the main partners.
Switzerland contributes financially to European nuclear fusion within the framework of its support to the EU's seventh research programme (2007-2013), which amounts to SFr8 million ($7.1 million) a year.
In September the Swiss Senate gave its full backing to the initiative. The House of Representatives is due to vote on the project shortly.
Around 100 researchers in Switzerland have also spent the past 15 years working on fusion projects linked to the ITER.
Institutions involved include the Centre for Research in Plasma Physics (CRPP) at the Federal Institute of Technology in Lausanne, the Paul Scherrer Institute in Villigen and Basel University's Institute of Physics.
Swiss expertise is being harnessed for the construction of microwave tubes to heat the hydrogen atoms, measuring equipment, superconductor cables and materials capable of withstanding constant bombardment by neutrons.
Despite decades of research and billions of dollars, the director of the CRPP, Minh Quang Tran, is certain that fusion energy is within our grasp.
"I'm pretty much convinced that within 30 years the DEMO reactor will start producing electricity and will be hooked up to the grid," he told swissinfo.
swissinfo, Simon Bradley in Geneva
To achieve nuclear fusion, atoms have to be heated to around 100 million degrees Celsius. At this temperature matter becomes a kind of "soup" of elementary particles, called plasma.
The fuel required – the elements Deuterium and Tritium – can be obtained from water and lithium, both found in abundance on Earth.
It is hoped that waste materials produced by nuclear fusion will lose their radioactivity after 100-200 years, unlike those from nuclear fission reactors which remain radioactive for thousands of years.
The ITER international organisation was established on October 24, 2007. Seven members are engaged in the project: China, the European Union, India, Japan, Korea, Russia and the United States, with the costs being shared by the seven members.
The principal goal of ITER is to generate 500 megawatts of fusion power for periods of 300 to 500 seconds with an input power of 50 megawatts.
ITER is being built in Cadarache, southern France on 180-hectare site. The experimental reactor will be 60 metres tall and weigh as much as an aircraft carrier. Some 300 people currrently work for ITER at Cadarache with 2,000 more researchers based around the world.
The demonstration reactor is expected to be operational in 2018. A commercial reactor is not expected before 2040.