Abingdon, Britain Twenty years after the world's first controlled release of nuclear fusion power took place, research is continuing into unlocking its potential as a safe and clean energy source for future generations.
“Fusion has all the advantages of nuclear power, but very few of the disadvantages,” says Remmelt Haange, deputy director general of the International Thermonuclear Experimental Reactor (ITER) research and development project.
However, fusion energy is not expected to be commercially available before 2050, when it would be competing with a strong showing from renewable energies.
The sun is a natural reactor for fusion power, a virtually limitless energy source.
The first human-initiated nuclear fusion reaction took place in 1952, when the first H-bomb was detonated.
But the world's first controlled release of fusion power was only staged on November 9, 1991, by the Joint European Torus (JET) in Abingdon, Britain, which houses the world's largest fusion device.
There is still no commercial fusion energy production plant in operation, but research is continuing into this technology, which can release huge quantities of energy by joining elements with a low atomic number (with a low number of protons in the nucleus of their atoms).
Scientists have learned that the most efficient reaction to create fusion power on Earth is what is called the DT fusion reaction, involving deuterium (D) and tritium (T).
The nuclei of the two hydrogen isotopes are forced together to overcome rejection due to their electric charge, producing a helium nucleus and a neutron, both with very high kinetic energy.
Deuterium can be easily produced from water, while tritium is extracted from liquid lithium.
However, fusion reactions between the two occur at a sufficient rate only in the heat of around 100 million degrees Celsius - nearly 10 times the temperature in the centre of the sun.
Human-initiated fusion needs to confine the hot plasma in what is termed a magnetic field cage, keeping it away from the material walls of the fusion chamber to prevent cooling, according to Germany's Max Planck Institute for Plasma Physics.
For the time being, the technology is not sufficiently developed to create fusion energy for commercial purposes.
The first controlled fusion in 1991 lasted around two seconds, releasing nearly two megawatts of energy, which does not even amount to one-tenth of the energy required to produce the hot plasma in the first place.
Six years later, 16 megawatts of fusion power were produced at JET from a total input power of 24 megawatts. That was a world record, but it nevertheless produced only two thirds of the initial energy required to heat the plasma.
It soon became clear that a larger and more powerful device would be necessary to demonstrate the feasibility of nuclear fusion energy on a reactor scale, leading to the ITER research and development project.
The world's largest and most advanced experimental nuclear fusion reactor is currently being built at Cadarache, southern France, with joint funding from the European Union, India, Japan, China, Russia, South Korea and the United States.
The fusion reactor is due to be completed by 2025, when scientists hope to produce 500 megawatts of output power for 50 megawatts of input power - or ten times the energy put in.
Advocates of the technology hope that fusion reactors can eventually replace fission reactors, where energy is generated by splitting elements of high atomic number.
Unlike the uranium used in fission reactors, fusion fuels are cheap and readily available, meaning there would be no dependency on individual producing countries.
Deuterium can be extracted from all forms of water and lithium - the lightest metallic element, which is needed to produce tritium - is plentiful in the Earth's crust.
It is estimated that if all the world's electricity were to be provided by fusion, known lithium reserves would last for at least one thousand years.
Fusion power stations would also be much safer than current nuclear sites. A core meltdown accident could not occur, fusion technology produces less radioactivity than fission technology, and no final waste storage sites would be needed.
However, critics of the technology question whether the investment in fusion power is worthwhile. The cost for ITER has spiralled from an initial estimate of 5 billion euros (6.9 billion dollars) to 16 billion - for a technology that is still decades away from any possible commercial application.
“Nuclear fusion won't be an economical option before 2050,” Greenpeace energy expert Heinz Smital says.
“By that time, we may have changed our entire energy production to renewable sources,” he added.
But while fusion may not be a general solution, it could be part of a mixed energy policy in the future, the ITER's Haange believes.
It is certainly worthwhile looking into “an energy source which is generated by fuels that are readily available around the world,” he muses. - Sapa-dpa