Fusion power usually brings to mind sprawling industrial complexes filled with massive lasers or powerful magnets. But a startup in Cambridge, Massachusetts, has been quietly building a desktop fusion device that can fit on a tabletop.
Cambridge Heavy Industries has been operating in stealth out of a small lab near MIT. Co-founder and CEO Yun Kai recently gave an exclusive look at the technology the company has been developing. Behind him during a video call, the optics of the device were clearly visible.
“We purposely built a small modular reactor. It’s tiny, it’s benchtop,” Kai said. “Because it’s small, it makes everything easier.”
That compact size has allowed Cambridge Heavy to experiment and iterate quickly. According to Kai, “The small module nature can enable 50 to 80 experiments, 50 to 80 shots per day.” Data from those experiments will feed simulations that use AI to optimize the design.
Why a Small Fusion Reactor Makes Sense
The nimble approach has attracted investor attention. Cambridge Heavy recently raised a $6.2 million seed round led by Azolla Ventures, with participation from Overlay, Neta Foundation, P3A, MassCEC, and the Rothrock family.
This desktop fusion device uses lasers to compress a fuel target, similar to the groundbreaking experiment that proved controlled fusion reactions could produce more power than they consume. But unlike other inertial confinement designs, Cambridge Heavy’s system minimizes the number of lasers required to spark fusion.
The system uses two main lasers to drive ignition. One laser is split into multiple beam lines that deliver light in concentric rings. Those rings of laser light are timed to hit the flat, round fuel target successively, starting from the outside and working inward. The first ring starts a compression wave within the target that begins traveling inward. Subsequent laser rings are timed to boost the wave at just the right moment to further compress the fuel.
As the shock wave reaches the center of the target, a laser fires on the target, generating heat and producing a magnetic field. With the right amount of pressure and heat, fusion occurs.
How the Technology Emerged
Cambridge Heavy’s design generates high pressures with relatively low laser power, according to Kai. The concept emerged from the lab of Keith Nelson, a chemist at MIT. There, researchers used laser pulses to study materials under extreme conditions. As they ramped up pressures, they realized they were approaching fusion-ready conditions.
The Road to a Fusion Power Plant
In about a decade, Cambridge Heavy plans to develop a power plant from the concept, though that will require scaling up the design. It will be larger than the current benchtop prototype, though not quite as large as other fusion power plants. Kai said it should be about the size of two basketball courts, and it will test whether the approach can generate enough energy to support a power plant.
Before that happens, Cambridge Heavy plans to use its smaller-scale devices to make tritium, a rare isotope of hydrogen that will be used by nearly all fusion power plants in the works today. Tritium sells for around $30,000 per gram today.
Each power plant won’t need a lot of tritium — on the order of grams per year — but the substance is so rare that only about 40 kilograms exist today. One recent study predicts that without new sources, the fusion power industry will be short by about 28 kilograms in 2054. At current prices, that’s about $840 million worth of tritium.
A Potential Revenue Stream While Pursuing Fusion
Fusion startups are in the process of designing fuel systems that will help reactors be largely self-sufficient when it comes to tritium supplies, though they may need occasional top-ups. But that process could take up to 10 years, Kai said, giving Cambridge Heavy years of potential revenue as it pursues its power plant.
What This Means for the Fusion Industry
Cambridge Heavy’s approach represents a notable shift in fusion research. While many companies pursue massive tokamak designs or enormous laser facilities, this startup is betting that smaller, faster iteration can accelerate progress.
The ability to run 50 to 80 experiments per day — rather than a handful per year at large facilities — could dramatically speed up learning cycles. Each experiment generates data that feeds into AI-driven simulations, helping the team refine the desktop fusion device more quickly than traditional approaches allow.
The focus on tritium production as an interim revenue stream is also strategically significant. With global supplies limited and demand expected to rise sharply as fusion plants come online, companies that can produce tritium economically may find a ready market. Cambridge Heavy’s smaller devices could serve this need while the company works toward its larger power plant design.
Whether this desktop fusion device ultimately leads to a commercial power plant remains to be seen. But the company’s progress suggests that the path to fusion may not require gigantic facilities. Sometimes, smaller really is better.
