World governments are signing off on the biggest and most expensive scientific experiment since the space station: a project to build an experimental nuclear fusion reactor. In this week's Green Room, the Iter programme's Director-General Nominee, Kaname Ikeda, argues that the considerable sums of money involved are a very worthwhile investment for the world.
The world faces a huge energy challenge in the coming years.
We need to develop other alternatives. This is the reason for research into developing fusion power
Not many people would disagree with that statement now, but how we meet that challenge is a matter for intense debate.
One thing is certain though - we need to rapidly develop our best options to tackle the problem, with estimates of energy needs indicating an increase of some 60% over the next two decades, due to projected growth in population and industrialisation of the developing countries.
Add to that the fact that currently over three-quarters of the world's energy is produced by burning fossils fuels producing CO2 and using up natural resources, and the need to develop new sources of energy that do not produce greenhouse gases becomes even more apparent.
Energy efficiency and renewables all have a role to play in tackling the problem, but they are unable to cover this demand alone.
Nuclear fission can help in bridging the gap, but its deployment faces political, technical and environmental concerns. If possible, we need to develop other alternatives. This is the reason for research into developing fusion power.
After decades of research in laboratories all over the world, a consortium of countries representing over half the world's population is now poised to take a major step forward in proving whether fusion power can become a reality.
On 21 November ministers from Europe, Japan, the People's Republic of China, India, the Republic of Korea, the Russian Federation and the United States of America meet in Paris to sign an agreement to construct an international experiment on the scale of a fusion power plant - Iter (International Thermonuclear Experimental Reactor; "the way" in Latin) in the South of France.
This truly global endeavour gives an indication of how seriously this research is being taken by governments of countries in all stages of development.
Fusion powers the Sun and stars. Our own Sun is an extremely large fusion reactor, but imitating the process down on Earth is far from easy.
...the problem of providing viable energy sources is not going to get easier even if conservation, CO2 sequestration, fission and renewables are more widely used...
To initiate the fusion reaction, hydrogen gas must be heated to over 100 million Celsius (10 times hotter than the core of the Sun), for the fuel particles to fuse rather than just bounce off each other's electrical charge in the resulting plasma.
The reaction uses two isotopes of hydrogen, deuterium and tritium, which produce helium, a neutron and very large amounts of energy.
One of the attractions of fusion is the tiny amount of fuel needed. The release of energy from a fusion reaction is 10 million times greater than from a typical chemical reaction, such as burning a fossil fuel.
A 1GW fusion power station would burn about 1kg of deuterium and tritium per day, compared with a 1GW coal power station burning 10,000 tonnes per day of coal.
The raw materials to produce this reaction are water and lithium. Lithium is a common metal, in daily use in mobile phones and laptop batteries.
Used to fuel a fusion power station, the lithium in one laptop battery, complemented by deuterium extracted from 45 litres of water, would produce some 200,000 kWh of electricity - the same as 40 tonnes of coal and the equivalent of the UK's current per capita electricity production for 30 years.
There is enough deuterium for millions of years of energy supply, and easily accessible lithium for several thousands of years.
Although it will occupy a large volume, around 1,000 cubic metres, the amount of tritium and deuterium in a fusion reactor will be tiny: the weight of the hot fuel in the core will be about the same as ten postage stamps.
The Iter project will be based at Cadarache, France
There is no possibility of a runaway reaction and because the gas will be so dilute, there is not enough energy inside the plant to drive a major accident and not much fuel would be available to be released to the environment if an accident did occur.
The aim of Iter is for the first time to put reactor scale physics and technology together in a single experiment to demonstrate that a fusion power plant is feasible.
The European experiment Jet, hosted in the UK, has already produced 16MW of fusion power, but only by inputting 25MW to heat the plasma.
Iter is double the dimensions of Jet, and has the goal of producing 500MW of fusion power, 10 times the input power.
Prototypes of all key Iter components have already been fabricated by industry and tested, and initial construction work for the 5bn-euro construction project is scheduled to start within the next year.
Another major challenge is to choose and test materials suitable to face the plasma in a fusion power station that can withstand continuous bombardment of neutrons, while at the same time being recyclable after a reasonable period for radioactive decay.
Iter cannot be used for this - it would need to be made of such materials - so the only way to test suitable materials is to reproduce the real environment of a power station by constructing an accelerator-based test facility, where material samples can be left in the neutron beam for many months to test their resilience.
The agreement to take such a facility - International Fusion Materials Irradiation Facility (IFMIF) - forward is due to be initialled the day after the signing of the ITER agreement.
The Jet plasma requires more energy input than it can output
This will be a joint Europe/Japan initiative, following up on from the broader approach strategy for fusion development agreed at the time of the Iter construction site choice between Europe and Japan.
If the Iter project and materials facility are successful, a prototype fusion power station could be putting electricity into the grid within 30 years, with commercial fusion power following 10 years later.
The longer view
Sceptics make the comment that fusion power has always been - and will always be - 50 years away - but the time horizon seems to be slightly shortening now.
One criticism levelled at fusion research is that it will not provide an energy source soon enough and that far too much money is being poured into a long-term gamble.
To put the cost into context, the current world energy market is about three trillion US dollars a year and growing. An energy source that can make an impact on that market, even at a few percent, has an annual market of tens of billions of dollars, several times the lifetime cost of the Iter experiment.
As for the timescale, fusion certainly wouldn't be available in the short-term, but the problem of providing viable energy sources is not going to get easier even if conservation, CO2 sequestration, fission and renewables are more widely used, and there are currently no other large-scale options beyond the 20-50-year timeframe.
We thus need to pursue fusion to the reactor scale through constructing Iter to see whether and to what extent it can contribute.
Kaname Ikeda is a nuclear engineer by training, and has also had a successful career in science and technology administration in Japan; as well as being a diplomat.
The Green Room is a series of opinion articles on environmental topics running weekly on the BBC News website
Do you agree with Kaname Ikeda? Is nuclear fusion a good investment for the world as it faces up to the energy and climate challenges of the 21st Century, or would the money be better spent on known clean technologies?