Commonwealth Fusion Systems: Racing Toward Net Energy
SPARC's rapid construction and breakthrough magnet technology mark a turning point in the fusion race, but challenges still loom ahead
Outside of Boston, in a rapidly expanding high-tech complex, Commonwealth Fusion Systems (CFS) is building what it hopes will be the first fusion device to achieve net energy, where more energy is generated than used. SPARC, the company’s tokamak-based fusion facility, is now more than 60% complete, with first plasma targeted for 2026 and full operational ramp-up by 2027.
“We’re heads down delivering that,” said Bob Mumgaard, Chief Executive of CFS. “We announced last year that the first commercial plant, which we call ARC, will be built in Virginia.”
At Fusion Fest in London on April 8, Mumgaard explained that SPARC could achieve an energy gain of 10, a significant leap demonstrating the commercial feasibility of magnetic confinement fusion. “Every day, they add more parts to it,” he said. “We hope to turn it on here in 2026 and start to ramp it in 2027.”
The goal is not just a scientific milestone—it’s a race to create an entirely new energy industry. “If you only build one fusion power plant, we have utterly failed,” he emphasised. “You need thousands.”
Magnet Technology
Central to CFS’s rapid progress is its mastery of high-temperature superconducting (HTS) magnets, which make compact, efficient fusion reactors possible.
“We actually build the magnets in-house,” Mumgaard explained. “It’s sort of an apex predator of technology. It needs a big ecosystem to work.”
HTS tape—thousands of kilometres of it—is used to create magnetic fields twice as strong as earlier materials. “Imagine you have a wire wrapped on a nail like in grade school,” he said. “But instead of one amp, it’s 50,000 amps. And the wire is made out of stuff that won a Nobel Prize.”
Over the past few years, CFS has expanded HTS tape production by a factor of 40.
“Most of that material for Sparc is actually now in warehouses, in magnets,” he added. As of this spring, about 80% of SPARC’s key toroidal field magnets had been manufactured.
These breakthroughs are backed by years of development. In 2021, CFS successfully tested the Toroidal Field Model Coil (TFMC) for steady magnetic fields, and in November 2024, the Central Solenoid Model Coil (CSMC) proved pulsed field operation under extreme conditions.
“When we hit the button and put current through the magnet, it performed like a champ,” Brandon Sorbom, CFS Co-Founder and Chief Science Officer, said in a press release. The CSMC achieved a record 5.7-tesla magnetic field and stored energy equivalent to five pickup trucks moving at highway speed.
“This is an important milestone on the road to commercialisation,” Sorbom added.
Building More Than Machines
CFS is not just creating a fusion reactor but building the foundation for a full-fledged fusion industry.
“The science doesn’t actually power the lights,” Mumgaard told the Fusion Fest audience. “You need plants that run every day, with people in them, finance behind them, supply chains, public acceptance, and regulation.”
Founded in 2018 as a spinout from MIT’s Plasma Science and Fusion Center, CFS has grown to over 1,300 employees and raised more than $2 billion—making it the largest private fusion company in the world.
The company’s structure is highly integrated. “We do the whole thing end-to-end because there’s a lot of value in integration,” Mumgaard said. “In the future, we’d love to hand off pieces. But right now, there’s no one else mature enough to hand it off to.”
CFS envisions fusion plants more like combined cycle gas plants than traditional nuclear reactors: tightly integrated, efficient, and modular. “It looks more like a combined cycle,” he said. “Less like hot rocks, more like engineered systems.”
However, building a supply chain for fusion remains daunting. SPARC’s components come from 30 countries, and global tensions complicate logistics. “It does worry me,” he admitted. “Fortunately for Sparc, a lot of the stuff is already in Massachusetts.”
He warned that broader geopolitical shifts could change the market landscape. “We’re moving from a globalisation framework to maybe more of a bifurcation framework,” he said. “All that still has to be determined.”
Fusion’s Urgency and Risks
For decades, fusion energy has been mocked as a technology perpetually “thirty years away.” Mumgaard directly challenged that mindset.
“There’s a general fallacy that something that’s always been a long way away, always will be a long way away,” he said. “People literally said flight would never happen—even when the Wright brothers were flying.”
Today, the fusion landscape looks very different. Scientific advances—such as LLNL’s ignition success at the National Ignition Facility—and technological improvements in magnets, simulations, and materials are converging to make fusion achievable within years, not decades.
“We have the science,” he said. “And now we have all these technologies flooding into fusion.” He compared the current moment to the early days of biotech: a chaotic, fertile period when major breakthroughs became inevitable.
If SPARC succeeds, it could achieve a gain of 15 megajoules by 2029 and be capable of scaling up to a gigajoule of fusion energy.
Asked how many other fusion technologies might also succeed soon, Mumgaard estimated, “One to two, maybe two to three.”
However, external pressures could threaten this momentum. The Trump administration’s proposed budget cuts to scientific research, including fusion-related programs like ARPA-E and Fusion Energy Sciences, could slow critical innovation.
“Private capital can accelerate deployment,” one industry expert noted. “But public funding underpins the foundational science that makes commercialisation possible.”
Fusion’s success depends on scientific prowess, continued investment, and policy support during this pivotal transition from lab experiments to power plants.
A New Energy Era Approaches
With SPARC approaching critical milestones, and ARC on track for the early 2030s, fusion’s transformation from science fiction to grid-connected reality is accelerating.
“This is about changing civilisation,” Mumgaard said. “Fusion offers energy that’s power-dense, sovereign, and manufactured. It’s not just another energy source—it’s something fundamentally different.”
The next few years are crucial for CFS. As the company finishes SPARC, navigates global supply chain challenges, and shapes a new industrial ecosystem, it is helping redefine the future of clean energy.
The dream of harnessing the power of the stars no longer belongs to a distant future. Thanks to companies like CFS, it’s starting to take form—right here, right now.