Last September, researchers at Commonwealth Fusion Systems slowly charged a 10-ton D-shaped magnet, pushing up the field strength until it surpassed 20 tesla—a record for a magnet of its kind. The company’s founders say the feat addressed the major engineering challenge required to develop a compact, inexpensive fusion reactor.

Fusion power has been a dream of physicists for decades. At temperatures well above 100 million degrees, as in the sun, atomic nuclei mash together, releasing a massive amount of energy in the process. If researchers can bring about these reactions in a controlled and sustained way here on Earth, it could provide a crucial source of cheap, always-on, carbon-free electricity, using nearly limitless fuel sources. 

In one approach, magnets are used to confine a gas of ions and electrons, known as a plasma, within doughnut-­shaped reactors. More powerful magnets mean less heat escapes and more fusion reactions can occur within a smaller, cheaper facility. And not by just a little: doubling the strength of the magnetic field reduces the volume of the plasma needed to generate the same amount of power by a factor of 16.

Despite decades of research and billions of dollars’ investment in the past, nobody has yet built a fusion plant that can produce more energy than it consumes. But Commonwealth and its backers are hopeful, and other fusion startups and research efforts have reported recent progress as well. 

Commonwealth is building a factory to mass-produce the magnets and laying the groundwork for a prototype reactor. If all goes as hoped, the startup plans to deliver fusion energy to the electric grid by the early 2030s.

As part of our 10 Breakthrough Technologies series, follow Commonwealth Fusion Systems’ attempts to make nuclear fusion a practical power source.