A pointed target positioner held the cylinder used in the fusion experiment.
Credit: NIF
SYDNEY: Scientists have recreated the intense temperatures and pressures at the centre of stars, a major milestone towards controlled nuclear fusion - potentially a limitless carbon-free source of energy.
"Demonstration of inertial fusion has the potential to lay out the path towards a limitless carbon-free source of energy," said lead researcher Siegfried Glenzer, from the National Ignition Facility in Livermore, California.
"[Inertial fusion] also produces the pressures and density-temperature conditions of the interior of the sun, allowing us to study solar physics and test astrophysical models," he added. Their study is published in today's online edition of Science.
Making a star on Earth
Inertial fusion ignition - where fuel is heated and compressed until it implodes, fusing individual atomic nuclei together and releasing energy - occurs naturally at the centre of stars.
Replicating the scorching temperatures and intense pressures of this process in a controlled, measurable way was one of the biggest obstacles to replicating fusion. But now Glenzer and his team have now proven this is possible.
They started with a low-energy pulse of laser light, shooting it through an amplification system the size of three football fields, and splitting it into 192 parallel beams.
Millions of degrees Celcius
These beams were then all fired at a small chamber less than one centimetre in length. For around 10 billionths of a second, 300 Terrawatts of laser power - which is more power than in the entire U.S. electrical grid - was injected into a tiny, empty capsule housed within this chamber, heating it to about 3.3 million degrees Celsius.
The researchers hope to create a real implosion later this year. In this experiment, the capsule will be filled with a dense fuel. An amplified laser pulse will be used to create a hot spot in the fuel, driving it to implode.
Energetic neutrons will escape as hydrogen isotopes fuse together, becoming helium. These helium particles will collide with the fuel, sparking a burning wave of fuel through the capsule.
As it burns, the fuel will spit out energetic moving neutrons. By capturing these neutrons, scientists will be able to harness the intense energy of nuclear fusion - the energy of stars.
"This advance represents a major step on the path towards achieving inertial fusion," said John Howard, a physicist from the Plasma Research Laboratories at the Australian National University in Canberra.
Technical hurdles remain, however. "Inertial fusion uses pulses of high power lasers to create small nuclear explosions in pellets of hydrogen," he explained.
"Many think this could be used to power the grid. To maintain steady generation of power, however, you need multiple pulses per a second. This repetition rate is a problem, as you need to replace the pellet," he cautioned.
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