This Startup Is Building a Two Meter Fusion Reactor that Can Power A City

Fusion energy has long been regarded as the “holy grail” of clean power. In theory, it offers abundant, carbon-free electricity from the same process that powers the sun. In practice, however, it has remained out of reach for decades.

The challenge lies in physics and engineering. Maintaining a stable plasma reaction is extremely difficult. Managing the intense heat generated inside the reactor adds another layer of complexity. At the same time, conventional reactor designs have tended to be large, intricate, and capital-intensive. Together, these barriers have slowed fusion’s path from laboratory research to commercial deployment.

Firefly Fusion is tackling these barriers with a more streamlined reactor design. The company is developing compact high-field tokamaks that rely on advanced superconducting magnets to confine the fusion reaction more effectively within a smaller structure. It also uses a plasma shaping approach called negative triangularity to improve how the plasma behaves during operation.

To better understand how they are doing it, we spoke to Rustem Ospanov, CEO of Firefly Fusion. This article contains notable highlights from our entire conversation.

This interview is part of our exclusive Scouted By GreyB series. Here, we speak with the founders of innovative startups to understand how their solutions address critical industry challenges and help ensure compliance with industry and government regulations. (Know more about startups scouted by GreyB!)

“If fusion is going to be affordable, the devices must be compact—and negative triangularity is what allows us to manage that high energy density safely.”

A Smaller, Smarter Tokamak: Firefly Fusion’s Bet on High-Field Magnets

Firefly Fusion combines advanced superconducting magnets with a carefully designed plasma shape to improve stability and manage extreme heat more effectively. The aim is to produce at least 5 times more fusion power (fusion gain>5) than the energy required to heat the plasma.

The company is targeting a commercially viable system capable of generating 50–100 megawatts of fusion power at capital costs comparable to modern power plants. Beyond electricity production, Firefly envisions its reactor as a development platform for testing materials, fuel cycles, and control technologies needed for next-generation fusion facilities.

How does Firefly Fusion differentiate itself from traditional fusion approaches?

Rustem: Traditional tokamaks are shaped like a donut and use magnetic fields to confine superheated hydrogen plasma. That’s not new. Tokamaks have been studied for decades. What changes the equation today is the availability of much stronger high-temperature superconducting magnets. These allow us to generate much higher magnetic pressure, which means we can shrink the reactor significantly while maintaining performance.

At Firefly, we combine that compact design with negative triangularity, a different plasma shape. Instead of the conventional “D” shape, we invert it.

Experiments in the US and Switzerland have shown that this configuration stabilizes the plasma edge and improves heat exhaust. For us, compactness brings affordability, and negative triangularity enables stable high-performance operation. It’s the combination that makes our approach unique.

What role do advanced magnets play in your reactor design?

Rustem: Magnets are central to fusion because they create the magnetic bottle that holds the plasma in place. Earlier superconductors could only reach about six tesla inside the tokamak. New high-temperature superconductors can reach 10 to 12 tesla, which is transformative.

Initially, we considered actively cooled copper magnets, but they require significant power and generate heat. As high-temperature superconductors became more commercially viable and prices dropped, we pivoted. Using these magnets allows us to achieve higher plasma pressure in a smaller volume. Of course, they require cryogenic cooling, so we design shielding layers to protect them from the intense heat produced during fusion.

Compact reactors sound efficient, but what trade-offs come with shrinking the system?

Rustem: When you make a reactor compact, the energy density increases. Fusion releases enormous heat, like hundreds of megawatts in a small volume. Managing that heat becomes a central challenge. With negative triangularity, we can distribute the heat more effectively across the exhaust region, reducing localized stress and instability.

Another trade-off is structural. These magnets exert forces so strong that they could theoretically lift an aircraft carrier. So we must design a robust magnetic cage using advanced materials to contain those forces safely within a smaller footprint. There’s also a physics risk, since negative triangularity is relatively new. Our strategy is to benchmark our simulations against experimental data from leading research tokamaks to reduce uncertainty.

You mentioned simulations showing strong performance. What benchmarks have you achieved digitally?

Rustem: Our simulations indicate we can produce 50 to 100 megawatts of fusion power while using five times less heating power, so a fusion gain above five. That means if we input 20–30 megawatts of heating power, we could generate over 100 megawatts of fusion power.

We’re also validating that this can be achieved in a compact device with a major radius of about two to two and a half meters. The next phase involves deeper simulations around heat exhaust systems, plasma control algorithms, wall materials, and diagnostics. Each of these systems must be optimized to move from digital validation to physical realization.

Beyond electricity, where do you see fusion making the biggest impact?

Rustem: The primary application is clean baseload electricity to complement renewables. Fusion reactors can provide grid stability without carbon emissions and without the same risk profile as fission. The fuel is more abundant, and the reaction is inherently safer because it’s easier to control.

There’s also potential for direct heat applications in industry—chemical processes or district heating in colder regions. In the longer term, fusion reactors can serve as platforms for neutron generation, material testing, and isotope production. But our main focus remains energy production.

Many say fusion is always decades away. Why do you believe this time is different?

Rustem: Fusion has been improving exponentially over the past 60 years. The progress is real. Now, we’re approaching a threshold where upcoming projects are expected to demonstrate net energy gain. Once that happens, the industry transitions from research to deployment.

We see the 2030s as the decade of scaling from proof-of-concept to full power plant systems. Firefly’s role is to build a compact, affordable platform that integrates all the technologies required for a commercial reactor. Science is ready, the community is energized, and investment interest is growing. That convergence makes this moment different.

What personally drives you to pursue fusion?

Rustem: There are three motivations. First, the science. When I look at experimental data and research papers, I see that negative triangularity works. That gives me confidence.

Second, the community. I work with scientists, engineers, and partners who believe this path is worth advancing. That collective conviction matters.

Third, the global need for clean energy. Traveling across Europe, Central Asia, and India, I see firsthand how critical energy security and sustainability are. Fusion has the potential to enable global prosperity with minimal environmental impact. That belief keeps me moving forward every day.

Meet our Interviewer – Raveena Singh, Senior Research Analyst at GreyB

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