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March 07, 2012

National Ignition Facility Laser Fusion Project approaches energy break-even point

This could be the year the National Ignition Facility (NIF) finally lives up to its name. The facility, which boasts the world’s largest laser, is designed to trigger fusion by imploding a target pellet of hydrogen isotopes, thereby releasing more energy than will go into the shot. NIF’s managers think that the end of their two-year campaign for break-even energy, or ‘ignition’, is in sight. “We have all the capability to make it happen in fiscal year 2012,” says Ed Moses, director of the US$3.5-billion facility, at the Lawrence Livermore National Laboratory in California.

Is NIF’s laser-based approach the best one? An interim report released on 7 March by a US National Academies panel concludes that it is still too early to tell, and recommends that fusion scientists explore alternative technologies for imploding the fuel.

The NIF team has made steady progress, however. When the push for ignition began 18 months ago, the facility was achieving 1% of the conditions thought to be needed for ignition. Now the figure stands at 10%, and the pace is quickening: a record 57 shots were taken in January alone. The team is also studying an array of tweaks, including encasing the fuel in beryllium or diamond instead of plastic and changing the hohlraum material or its shape. Moses says that it might also be possible to crank up NIF’s peak energy from the 1.8 megajoules estimated to be needed for break-even to 2.2 megajoules.


Engineers inspect the fusion chamber at the National Ignition Facility. LLNL




The $460 million requested for the NIF effort in 2013 will allow it to vary its approach. For example, plasma physicists at the University of Rochester in New York want to adapt NIF’s lasers so that they can implode a hydrogen-isotope pellet directly and dispense with the hohlraum.

The NIF scientists aren’t waiting for alternative approaches to catch up, however. Even before achieving ignition, they are racing to plan their next project, a demonstration power plant that they call LIFE, for Laser Inertial Fusion Energy. To be economic, the plant would have to produce more than 50 times more energy from each shot than it puts in, and would have to boost repetition rates from a few shots a day to 15 per second — no mean feat.

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