Science News

Fusion experiment breaks crucial energy

Tue, 18th Feb 2014

Hannah Critchlow

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Powerful lasers have managed to trigger a controlled fusion reaction that releases more energy than was absorbed by the fuel. It marks a nuclear reactionkey milestone in the quest to generate useful power by squashing together the nuclei of atoms.

The National Ignition Facility (NIF) in Livermore, California, uses 192 high-powered lasers to fuse deuterium and tritium – heavy isotopes of hydrogen - inside a fuel pellet the size of a pea.

This pellet is held inside a gold container called a hohlraum. When the lasers hit the hohlraum, it creates a burst of X-rays that force the fuel pellet to implode, reaching millions of degrees and crushing the nuclei inside until they fuse – a process that converts some of their mass into energy.

For the first time, the experiments have released more energy from the fuel than was put in by the X-rays – about 1.2 to 1.9 times more. Although this amounts to only 1% of the original laser energy, because most of that was absorbed by the hohlraum

To achieve true ‘ignition’, there would have to be an overall energy gain. Researchers at NIF boosted the energy yield of the fusion reaction by tuning the lasers so that they delivered more of their energy earlier in the pulse.

This made the fuel pellet less unstable as it imploded, and also prevented some of the energetic fusion debris from escaping, so that it could help to trigger more fusion reactions. It’s an important milestone for NIF, which has struggled to reach key goals such as this.

Last year, NIF’s research programme was restructured so that it spends more time doing nuclear weapons research, with the aim of keeping warheads safe and reliable without needing detonation tests.

Meanwhile, the world’s biggest fusion project, ITER, is still likely to be the first reactor to produce substantially more energy than is put in. This giant, donut-shaped reactor, which will contain its fuel within powerful magnetic fields, is being built in Cadarache, France. With a budget of €15 billion, project managers hope it will start to generate power in 2028.



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To approach being a practical energy source, the National Ignition Facility will need to increase its rate to perhaps hundreds of laser shots per second.
At present they can achieve around 2 shots per day, with a laborious inspection process after each shot. Skipping the inspection step could cause one of the laser amplifiers to explode on the next shot - the energies involved are incredibly high.

Magnetic confinement, the other major approach to controlled fusion, is working towards a very large demonstration project at ITER.

There has been some theoretical analysis recently about combining magnetic and laser heating. evan_au, Sun, 16th Feb 2014

This sounds like an important milestone in the search for practical exploitation of fusion - "proof in principle" is now established, and future progress towards harnessing similar reactions to those used by stars is possibly inevitable. It is unfortunate the the recent "Jade rabbit" rover on our moon has suffered a mishap - especially since the moon is a far richer (potentially) source of Tritium than Earth, useful in fusion reactors (from memory, Tritium is more efficient that fusing hydrogen)  :) Ian Scott ZL4NJ, Mon, 17th Feb 2014

As a practical source of power I have always considered ITER type fusion reactors a wild pipe dream what can we say about laser types they make ITER types mundane and practical in comparison !
I remember well when the Sellafeild  Plutonium plant was coaxed into producing 20GW we had he worlds first revolutionary nuclear power station.
Laser fusion can only be a thinly disguised military project as for producing power its nonsense. syhprum, Mon, 17th Feb 2014

Enough said? They would need to be able to ignite roughly 40-50% MORE fuel in ONE burst in order to produce more energy than was put in, as said in the OP. I still believe that magnetic fusion is A LOT more promising if they can create a self sustaining reaction, then over time it would produce more than it took to start the reaction, although then the problem is learning to stop the reaction quickly incase of emergency! THAT would be a big explosion! crimsonknight3, Mon, 24th Feb 2014

I answered myself about the quick stopping in case of an emergency already lol, if the magnetic field broke down it would damage the interior of the reactor contaminating the reaction and stopping it crimsonknight3, Mon, 24th Feb 2014

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