Cambridge Heavy Industries Builds a Desktop Fusion Reactor for Tritium Production

Nuclear fusion usually conjures images of massive industrial facilities — enormous lasers, superconducting magnet rings, complexes that would take up whole city blocks. But Cambridge Heavy Industries, a startup operating in stealth for months in a small lab near MIT in Cambridge, Massachusetts, has a different vision: a fusion reactor that fits on a laboratory benchtop.

The company was publicly revealed during TechCrunch Disrupt 2026, when its co-founder and CEO, Yun Kai, gave TechCrunch an exclusive glimpse of the technology he has been developing. "We purposely built a small modular reactor. It is tiny, it is benchtop," Kai said. "Because it is small, everything becomes easier."

The technology behind the device

Cambridge Heavy's design is based on inertial confinement fusion — the same scientific approach that the National Ignition Facility (NIF), the world's largest laser facility at Lawrence Livermore National Laboratory, used to prove in December 2022 that controlled fusion reactions could produce more energy than consumed.

Yet while NIF uses 192 giant laser beams arranged in every direction to compress a fuel capsule, Cambridge Heavy's approach is radically different. The system uses only two main lasers. One of them is split into multiple beam lines delivering light in concentric rings. These rings of light are timed to strike a flat, round fuel target successively, starting from the outside and working inward.

The first ring initiates a compression wave inside the target that travels inward. The subsequent rings are timed to boost that wave at just the right moment, further compressing the fuel. When the shockwave reaches the center of the target, a laser fires on the target, generating heat and producing a magnetic field. With the right pressure and heat, fusion occurs.

The concept emerged from the laboratory of Professor Keith Nelson, a chemist at MIT, where researchers used laser pulses to study materials under extreme conditions. As they ramped up pressures, they realized they were approaching fusion-ready conditions.

50 to 80 shots per day

The advantage of the small size is that Cambridge Heavy can perform 50 to 80 experiments per day — an iteration pace impossible for larger facilities, which operate with only one or two shots per day. Each shot generates data that feeds artificial intelligence simulations to continuously optimize the design.

"The small modular nature can enable 50 to 80 experiments, 50 to 80 shots per day," Kai explained. This accelerated cadence is what sets Cambridge Heavy apart from other fusion companies, which spend weeks or months between successful experiments.

The tritium market: a silent bottleneck

This is the question that makes Cambridge Heavy particularly relevant. Nearly every fusion power plant in development — from Commonwealth Fusion Systems, which is building the SPARC tokamak in Massachusetts, to Helion, which already signed the world's first agreement to supply fusion electricity to Microsoft — use deuterium-tritium fuel. And tritium is extraordinarily rare.

There are only about 40 kilograms of tritium in the entire world, valued at approximately $30,000 per gram, which totals about $840 million in global reserves. For context: a single 1 GW fusion reactor would require roughly 55 kg of tritium per year, and recent studies predict that without new sources, the fusion industry will face a deficit of approximately 28 kg by 2054.

This means that the fusion plants being designed today will need tritium to start operating — and that fuel simply does not exist in sufficient scale.

Cambridge Heavy doesn't intend to solve the long-term energy generation problem first. It wants to solve the tritium problem now. Its benchtop reactor will be used to produce tritium as a primary product, generating revenue in the coming years while the company pursues its long-term goal: building an energy plant the size of two basketball courts, in about a decade.

Funding and ambition

Cambridge Heavy's approach has already attracted investors. The company recently raised a $6.2 million seed round led by Azolla Ventures, with participation from Overlay, Neta Foundation, P3A, MassCEC, and the Rothrock family. The startup is headquartered at The Engine, Anjin Technology's deep-tech incubator.

The company's design uses off-the-shelf equipment — conventional laser and optics equipment — meaning the supply chain is the existing laser and optics industry, not specialized nuclear suppliers.

While Commonwealth Fusion Systems and other companies struggle with reactors dozens of meters in diameter, Cambridge Heavy is proving that fusion can be done at benchtop scale. If the approach works in the coming years, it could open the way to a new fusion fuel production economy — and perhaps accelerate the arrival of clean, virtually unlimited energy that has always been humanity's dream.

Sources: TechCrunch, Dealroom, RSIS

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