By Richard Gray, Science Correspondent
Last Updated: 4:50PM GMT 27 Dec 2008
While it has seemed an impossible goal for nearly 100 years, scientists now believe that they are on brink of cracking one of the biggest problems in physics by harnessing the power of nuclear fusion, the reaction that burns at the heart of the sun.
In the spring, a team will begin attempts to ignite a tiny man-made star inside a laboratory and trigger a thermonuclear reaction.
Its goal is to generate temperatures of more than 100 million degrees Celsius and pressures billions of times higher than those found anywhere else on earth, from a speck of fuel little bigger than a pinhead. If successful, the experiment will mark the first step towards building a practical nuclear fusion power station and a source of almost limitless energy.
At a time when fossil fuel supplies are dwindling and fears about global warming are forcing governments to seek clean energy sources, fusion could provide the answer. Hydrogen, the fuel needed for fusion reactions, is among the most abundant in the universe. Building work on the £1.2 billion nuclear fusion experiment is due to be completed in spring.
Scientists at the National Ignition Facility (NIF) in Livermore, nestled among the wine-producing vineyards of central California, will use a laser that concentrates 1,000 times the electric generating power of the United States into a billionth of a second.
The result should be an explosion in the 32ft-wide reaction chamber which will produce at least 10 times the amount of energy used to create it.
"We are creating the conditions that exist inside the sun," said Ed Moses, director of the facility. "It is like tapping into the real solar energy as fusion is the source of all energy in the world. It is really exciting physics, but beyond that there are huge social, economic and global problems that it can help to solve."
Inside a structure covering an area the size of three football pitches, a single infrared laser will be sent through almost a mile of lenses, mirrors and amplifiers to create a beam more than 10 billion times more powerful than a household light bulb.
Housed within a hanger-sized room that has to be pumped clear of dust to prevent impurities getting into the beam, the laser will then be split into 192 separate beams, converted into ultraviolet light and focused into a capsule at the centre of an aluminium and concrete-coated target chamber.
When the laser beams hit the inside of the capsule, they should generate high-energy X-rays that, within a few billionths of a second, compress the fuel pellet inside until its outer shell blows off.
This explosion of the fuel pellet shell produces an equal and opposite reaction that compresses the fuel itself together until nuclear fusion begins, releasing vast amounts of energy.
Scientists have been attempting to harness nuclear fusion since Albert Einstein’s equation E=mc², which he derived in 1905, raised the possibility that fusing atoms together could release tremendous amounts of energy.
Under Einstein’s theory, the amount of energy locked up in one gram of matter is enough to power 28,500 100-watt lightbulbs for a year.
Until now, such fusion has only been possible inside nuclear weapons and highly unstable plasmas created in incredibly strong magnetic fields. The work at Livermore could change all this