In a breakthrough experiment, nuclear fusion finally makes more energy than it uses

Scientists have finally managed to bottle the sun.

At 1:03 a.m. PST on December 5, researchers with the National Ignition Facility in Livermore, Calif., ignited controlled nuclear fusion that, for the first time, resulted in the net production of energy. A 3-million-joule burst emerged from a peppercorn-sized capsule of fuel when it was heated with a 2-million-joule laser pulse. Details of the long-awaited achievement, which mimics how the sun makes energy, were revealed in a news conference December 13 by U.S. Department of Energy officials.

“This is a monumental breakthrough,” says physicist Gilbert Collins of the University of Rochester in New York, who is a former NIF collaborator but was not involved with the research leading to the latest advance. “Since I started in this field, fusion was always 50 years away…. With this achievement, the landscape has changed.”

Fusion potentially provides a clean energy source. The fission reactors now used to generate nuclear energy rely on heavy atoms, like uranium, to release energy when they break down into lighter atoms, including some that are radioactive. While it’s comparatively easy to generate energy with fission, it’s an environmental nightmare to deal with the leftover radioactive debris that can remain hazardous for hundreds of millenia.

Controlled nuclear fusion, on the other hand, doesn’t produce such long-lived radioactive waste, but it’s technically much harder to achieve in the first place. In nuclear fusion, light atoms fuse together to create heavier ones. In the sun, that typically occurs when a proton, the nucleus of a hydrogen atom, combines with other protons to form helium. 

Getting atoms to fuse requires a combination of high pressure and temperature to squeeze the atoms tightly together. Intense gravity does much of the work in the sun. 

At the National Ignition Facility, 192 lasers directed at a small capsule filled with deuterium and tritium, heavy types of hydrogen, provided a blast of energy that did the trick instead. About 4 percent of that fuel was fused in the process. The new result far surpassed the 1.3 million joules of energy produced by an earlier NIF experiment that marked the first time the team managed to ignite nuclear fusion.

“These recent results [at] NIF are the first time in a laboratory anywhere on Earth [that] we were able to demonstrate more energy coming out of a fusion reaction than was put in,” NIF physicist Tammy Ma said at the news conference. She predicted that pilot projects for power plants based on the fusion approach will be built in the “coming decades.”

But this latest fusion burst still didn’t produce enough energy to run the laser power supplies and other systems of the NIF experiment. It took about 300 million joules of energy from the electrical grid to get a hundredth of the energy back in fusion.

“The net energy gain is with respect to the energy in the light that was shined on the target, not with respect to the energy that went into making that light,” says University of Rochester physicist Riccardo Betti, who was also not involved with the research. “Now it’s up to the scientists and engineers to see if we can turn these physics principles into useful energy.”

Despite that, it’s a potential turning point in the technology comparable to the invention of the transistor or the Wright brothers’ first flight, says Collins. “We now have a laboratory system that we can use as a compass for how to make progress very rapidly,” he says.