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Scientists achieve nuclear fusion with giant laser

A successful nuclear fusion process could help solve the world's energy problems

Researchers at the Lawrence Livermore National Laboratory Wednesday said they've achieved a first: A nuclear fusion system has produced more energy than it initially absorbed.


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The interior of the NIF laser target chamber. The service module carrying technicians can be seen on the left. The target positioner, which holds the target, is on the right.

The research, published in the peer reviewed journal Nature, involved a petawatt power laser used to try to ignite fusion plasma fuel in a confined space. Each pulse of the laser, which delivered peak power of 1,000,000,000,000,000 watts, lasted less than 30 femtoseconds, or 0.00000000000003 seconds.


A fusion reaction is markedly different from fission reactions that are used in today's nuclear reactors. Instead of splitting atoms as fission does, fusion bonds atoms.

With fusion, only a tiny amount of fuel is present at any given time (typically about a milligram), according to Mike Dunne, director for Laser Fusion Energy at Lawrence Livermore Labs.

The laser, known as the National Ignition Facility (NIF), uses 192 beams 300 yards long that focus on a fuel cell about the diameter of a No. 2 pencil.

The hohlraum
A metallic case called a hohlraum holds the fuel capsule for NIF experiments. Target handling systems precisely position the target and freeze it to cryogenic temperatures (18 kelvins, or -427 degrees Fahrenheit) so that a fusion reaction is more easily achieved.

While powerful, the laser has not yet been able to ignite the plasma fuel. When and if it does, the fuel would begin to burn in a self-sustaining reaction to such a degree that it will produce a megajoule of energy.

Producing that staggering amount of energy could help to solve the world's energy issues.

"Think of it like the gas in the piston chamber of your car, where the idea is to ignite all the fuel to produce an efficient burn. So it is 'self-sustaining' but can never be 'run-away.' In the case of laser fusion, the burn time is incredibly short - typically a few tens of picoseconds," Dunne said in an email to Computerworld.

The researchers' latest victory marks the accomplishment of a key goal on the way to plasma fuel ignition: the project generated energy through a fusion reaction that exceeded the amount of energy deposited into deuterium-tritium fusion fuel and hotspot during the implosion process, "resulting in a fuel gain greater than unity," the team stated in the Nature article.

"Ignition is the ultimate goal of the experiments, so the latest result marks a waypoint on the way to that point (albeit quite a significant waypoint)," Dunne said.

Hohlraum clyinder

The next significant step for the research is to achieve an "alpha burn," where the fusion output more than doubles the energy input to the fuel. In an alpha burn, the researchers hope to pass a particular threshold of energy output -- specifically 10,000,000,000,000,000 fusion reactions.

"We are currently a few percent below this value," Dunne said.

Once ignition is achieved, it promises a path toward a sustainable, environmentally sound energy source that would exceed that of any previously created.

"There are a number of possible paths forward," Dunne said, "and it will require a close partnership between industry and government. But in principle, because the NIF was built at the same scale as the fusion performance needed for a power plant, the leap is not as great as you may think."

Dunne believes that once nuclear fusion energy is achieved, there will be an overriding push to capitalize on the success of it.

"It is, after all, often called the 'holy grail' of energy sources," he said.


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