Cambridge Heavy Industries is building a tabletop fusion device that compresses a fuel target with lasers. The startup, based in Cambridge, Massachusetts, plans to make tritium with smaller versions of the system. This rare hydrogen isotope is expected to be needed by nearly all fusion power plants now in development. The company has described its design and plans, but it has not said it has produced tritium yet.
The company has been operating in stealth from a small lab near MIT, where co-founder and CEO Yun Kai gave TechCrunch an exclusive look at its technology. Kai said the team chose a small, modular reactor on purpose: “We purposely built a small modular reactor. It’s tiny, it’s benchtop,” he said. “Because it’s small, it makes everything easier.”
Its compact size allows the team to test ideas and make changes quickly. Kai said the device could enable 50 to 80 experiments, or “shots,” each day. Data from those experiments will feed simulations that use AI to optimize the design. Cambridge Heavy recently raised a $6.2 million seed round led by Azolla Ventures, with Overlay, Neta Foundation, P3A, MassCEC, and the Rothrock family also participating.
The reactor’s lasers compress a fuel target, using the broad approach of a groundbreaking experiment that showed controlled fusion could generate more power than it consumed. Unlike other inertial-confinement systems, Cambridge Heavy’s design minimizes the number of lasers needed to trigger fusion.
Ignition is driven by two main lasers. One is split into multiple beam lines, which send light toward a flat, round target in concentric rings. The rings hit one after another, from the outside inward. The first creates a compression wave within the target that travels inward. The subsequent rings are timed to boost the wave at just the right moment and compress the fuel further. As the shock wave reaches the center, a laser fires on the target, generating heat and producing a magnetic field. Fusion takes place with the right amount of pressure and heat.
Kai said the design can create high pressures without requiring much laser power. The idea grew out of work in the lab of Keith Nelson, a chemist at MIT. Researchers there used laser pulses to study materials under extreme conditions. As they ramped up pressures, they realized they were approaching fusion-ready conditions.
In about a decade, Cambridge Heavy plans to develop a power plant from the concept, which will mean scaling up the design. The plant would exceed the size of the current benchtop prototype, while remaining smaller than other fusion power plants. Kai put its planned size at about two basketball courts. The plant will test whether the approach can generate enough energy to support a power plant.
In the meantime, the company plans to make tritium with smaller devices. Each power plant will need only a small amount of the isotope, on the order of grams per year, yet just about 40 kilograms exist today. Tritium sells for around $30,000 per gram.
A recent study estimates that the fusion power industry could be short by about 28 kilograms in 2054 if no new sources emerge. At current prices, that shortfall would be worth about $840 million.
Fusion startups are developing fuel systems to make their reactors largely self-sufficient in tritium, although they may still need occasional top-ups. Kai said the process of developing those systems could take up to 10 years, giving Cambridge Heavy years of potential revenue as it pursues its power plant. Whether its compact laser platform can produce tritium in practice remains an open engineering question.
