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Cambridge startup takes big step toward clean fusion power

A team of engineers and scientists from CFS and MIT’s PSFC lower the superconducting magnet into the test stand in which the magnet was cooled and powered to produce a magnetic field of 20 tesla.Commonwealth Fusion Systems

It’s one of the oldest jokes in science: “Nuclear fusion will always be 20 years away.”

But on Wednesday, scientists at the startup Commonwealth Fusion Systems in Cambridge said they’ve moved up the timeline by a decade, thanks to a breakthrough that could potentially have clean-running fusion plants online by the early 2030s.

In partnership with the Massachusetts Institute of Technology, CFS has successfully tested the world’s most powerful superconducting magnet, capable of containing the immense energy of a fusion reaction — in which atoms are joined together — while consuming far less power than earlier magnets. As a result, the CFS magnet would enable the construction of fusion power plants that could produce more energy than they consume, making them practical for commercial use.


“This test provides reason for hope that in the not too distant future we could have an entirely new technology to deploy in the race to transform the global energy system and slow climate change,” said Maria Zuber, MIT’s vice president for research.

Like today’s nuclear fission plants, fusion plants could generate electricity without emitting planet-warming carbon. But fusion reactors also would produce hardly any radioactive waste, would pose no risk of meltdowns, and could be switched on and off as needed. And fusion runs on deuterium, an isotope of hydrogen that is readily obtained from seawater, meaning there could be a practically unlimited fuel supply.

Fusion is the same energy source that powers the sun, and hydrogen bombs. Scientists have spent decades seeking a way to unleash this power while keeping it under control. The most common approach, called a “tokamak,” was first conceived by scientists in the Soviet Union. A tokamak is a giant donut-shaped electromagnet that generates a field so strong that fusion reactions can safely take place inside the field. Tokamaks have achieved successful fusion reactions, but they use more power than they generate, and the machines are immensely expensive. For instance, an international consortium is spending $25 billion to construct the biggest tokamak ever. Under construction in France, it’s not expected to switch on until 2025.


That’s when Commonwealth expects to activate SPARC, an experimental reactor under construction in Devens. SPARC is intended to be the first fully successful fusion reactor, capable of putting out a steady supply of clean energy.

“That’s a big Kitty Hawk moment,” said CFS chief executive Bob Mumgaard.

CFS was spun out of MIT in 2018 and has raised more than $200 million from investors including European energy companies Eni and Equinor, Silicon Valley firm Khosla Ventures, and the Bill Gates-founded investment firm Breakthrough Energy Ventures.

The CFS magnet, which weighs about 10 tons, is tiny by tokamak standards. It derives its power from the use of superconducting materials that conduct electricity without any loss of energy. Earlier tokamaks used conventional copper-based electromagnets, which conduct electricity far less efficiently and must be built much bigger.

Dennis Whyte, director of MIT’s Plasma Science and Fusion Center, said that an earlier copper-based tokamak needed 200 million watts of power to produce an adequate magnetic field. By using superconductors, the new CFS magnet achieves the same magnetic strength but with just 30 watts.

“The goal is a power plant the size of a high school gym,” said Zuber, “that produces as much power as a coal plant, with zero carbon.”


Matthew Moynihan, a former senior nuclear engineer at the US Naval Nuclear Laboratory and founder of fusion consulting firm NLF Consultants, thinks CFS could well achieve its 10-year goal.

“They’re using a lot of existing work, about 70 years of existing research, but then combining it with mind-bogglingly strong magnets,” said Moynihan. “It’s an entirely new class of fusion reactor, one the world has never worked with before.”

Hiawatha Bray can be reached at hiawatha.bray@globe.com. Follow him @GlobeTechLab.