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In October 2010, in a building the size of three U.S. football fields, researchers at the Lawrence Livermore National Laboratory powered up 192 laser beams, focused their energy into a pulse with the punch of a speeding truck, and fired it at a pellet of nuclear fuel the size of a peppercorn. So began a campaign by the National Ignition Facility (NIF) to achieve the goal it is named for: igniting a fusion reaction that produces more energy than the laser puts in.

A decade and nearly 3000 shots later, NIF is still generating more fizz than bang, hampered by the complex, poorly understood behavior of the laser targets when they vaporize and implode. But with new target designs and laser pulse shapes, along with better tools to monitor the miniature explosions, NIF researchers believe they are close to an important intermediate milestone known as “burning plasma”: a fusion burn sustained by the heat of the reaction itself rather than the input of laser energy.

Self-heating is key to burning up all the fuel and getting runaway energy gain. Once NIF reaches the threshold, simulations suggest it will have an easier path to ignition, says Mark Herrmann, who oversees Livermore’s fusion program. “We’re pushing as hard as we can,” he says. “You can feel the acceleration in our understanding.” Outsiders are impressed, too. “You kind of feel there’s steady progress and less guesswork,” says Steven Rose, co-director of the Centre for Inertial Fusion Studies at Imperial College London. “They’re moving away from designs traditionally held and trying new things.”

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