Thirteen years after completion of the $3.5 billion National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL), the goal embodied in the giant laser’s name has finally been achieved. For the first time in the nearly 70-year history of controlled fusion research, a fusion reaction has yielded more energy than it took to spark it.
According to Mark Herrmann, program director for weapons physics and design at LLNL, a laser shot performed on 5 December produced about 3.15 megajoules of fusion energy from the 2.05 MJ of laser light that reached the small cylindrical chamber known as a hohlraum, which converts the UV to x rays. Suspended inside was a diamond-coated, peppercorn-size capsule containing deuterium–tritium fuel, which the x rays imploded.
The results were officially announced by Energy secretary Jennifer Granholm, Office of Science and Technology Policy director Arati Prabhakar, and other officials on 13 December. The findings have not been peer reviewed, and Herrmann says he would have preferred they be released through a scientific journal. But the results were sure to leak out, and it was important that the advance be reported correctly, he adds.
The yield surpasses the criteria for ignition established by the National Research Council in 2007. By other measures, such as the amount of energy deposited on the fuel capsule—around 250 kilojoules—the gain, or Q, is around 10, says Michael Campbell, who led NIF construction until 1999. Yet the amount of fusion energy from the record shot amounts to just 1% of the 300 MJ from the grid that’s required to power the 192-beam NIF laser, Herrmann says. Thus, although the lab’s achievement is a significant step, inertial fusion is still a long way from becoming a viable energy source.
Ignition is a key process in nuclear weapons, says Herrmann, and will enable experiments in which materials can be exposed to highly intense fluxes of the 14 MeV neutrons that are produced in fusion reactions. That, he says, has direct application to maintaining the weapons stockpile—NIF’s primary mission.
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