Fusion energy is the ultimate clean-energy dream. It’s what powers the sun. Researchers have been trying for decades to mimic that process. But creating what amounts to a miniature star that can be hooked up to the electrical grid has been an expensive, grindingly slow, often frustrating process, with electricity from fusion always seemingly at least a couple of decades away.

But now there has been a breakthrough. It happened Dec. 5 at the National Ignition Facility, a part of the Lawrence Livermore National Laboratory in California. It required a facility the size of a sports stadium and one the most powerful laser arrays in the world. On Tuesday, officials with the Energy Department announced that the experiment had succeeded in creating a fusion reaction with “net energy gain.”

For the experiment, 192 lasers converged on a tiny capsule containing a pellet of hydrogen, compressing atomic nuclei and generating a fusion reaction that produced more output of energy (a little more than three megajoules) than was put in by the lasers (about two).

Scientists involved in fusion research across the planet hailed this as a major breakthrough — the first successful “ignition” of fusion in a laboratory.

Here is how they did it.

The breakthrough at Livermore was a huge step in showing that engineers can create a controlled nuclear fusion reaction that is potentially self-sustaining. However, scientists are clear that they face many daunting challenges in turning fusion into a practical, safe and abundant source of electric power.

Input

2.05 MJ

Output

3.15 MJ

Energy to generate the laser beams

300 MJ

Input

2.05 MJ

Output

3.15 MJ

Energy to generate the laser beams

300 MJ

For example, the laser used to start ignition injected 2.05 megajoules of energy and yielded 3.15 megajoules of output, proving that more power can result from less used. But the facility needed 300 megajoules of power to create the laser beams in the first place. Moreover, it was not designed to create electricity. This was a science experiment more than a demonstration of a practical technology.

Still, the achievement bolsters fusion’s potential as a tool for one day delivering a carbon-free future.

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