One step closer to a laser-powered fusion reactor.

Science magazine celebrates a test result from the National Ignition Laboratory that brings us all one step closer to cheap, clean energy by using lasers to compress a “fuel capsule” hard enough that it began fusing its atoms together:

Last week, a single laser shot sparked a fusion explosion from a peppercorn-size fuel capsule that produced eight times more energy than the facility had ever achieved: 1.35 megajoules (MJ)—roughly the kinetic energy of a car traveling at 160 kilometers per hour. That was also 70% of the energy of the laser pulse that triggered it, making it tantalizingly close to “ignition”: a fusion shot producing an excess of energy.

“After many years at 3% of ignition, this is superexciting,” says Mark Herrmann, head of the fusion program at Lawrence Livermore National Laboratory, which operates NIF.

NIF’s latest shot “proves that a small amount of energy, imploding a small amount of mass, can get fusion. It’s a wonderful result for the field,” says physicist Michael Campbell, director of the Laboratory for Laser Energetics (LLE) at the University of Rochester.

NIF’s approach, known as inertial confinement fusion, uses a giant laser housed in a facility the size of several U.S. football fields to produce 192 beams that are focused on a target in a brief, powerful pulse—1.9 MJ over about 20 nanoseconds. The aim is to get as much of that energy as possible into the target capsule, a diminutive sphere filled with the hydrogen isotopes deuterium and tritium mounted inside a cylinder of gold the size of a pencil eraser. The gold vaporizes, producing a pulse of x-rays that implodes the capsule, driving the fusion fuel into a tiny ball hot and dense enough to ignite fusion. In theory, if such tiny fusion blasts could be triggered at a rate of about 10 per second, a power plant could harvest energy from the high-speed neutrons produced to generate electricity.

When NIF launched, computer models predicted quick success, but fusion shots in the early years only generated about 1 kilojoule (kJ) each. A long effort to better understand the physics of implosions followed and by last year shots were producing 100 kJ. Key improvements included smoothing out microscopic bumps and pits on the fuel capsule surface, reducing the size of the hole in the capsule used to inject fuel, shrinking the holes in the gold cylinder so less energy escapes, and extending the laser pulse to keep driving the fuel inward for longer.