Realta Fusion shows its mirror reactor can pull electricity straight from plasma

Why it matters

Realta Fusion's demo is not net power, but it gives Kieran Furlong a concrete hardware proof point for a fusion architecture built around efficiency and industrial deployment, just as the company is raising again.

Kieran Furlong and Realta Fusion have demonstrated direct energy conversion on a working fusion-plasma machine, a small but useful proof point for the Madison, Wisconsin startup's bet that an old reactor geometry can be made economically relevant with modern magnets.

The company said in a June 30 blog post that, on June 19, it used the Wisconsin HTS Axisymmetric Mirror, known as WHAM, to convert kinetic energy from plasma particles into electricity. TechCrunch reported that the experiment powered lightbulbs and that Realta Fusion believes it is the first private fusion company to publicly demonstrate direct energy conversion applied to a fusion plasma.

That claim should be read precisely. Realta Fusion did not demonstrate net electricity production. Realta Fusion did not show a commercial plant producing large-scale power from fusion-born particles. The company’s own framing is explicit that the WHAM demo was a prototype-scale result, not a net-electricity breakthrough.

The point is not that Realta Fusion has built a power plant. The point is that Realta Fusion has shown a piece of the power-plant architecture that Furlong has been pitching since spinning the company out of University of Wisconsin-Madison research: a compact magnetic mirror system that could recycle some of the energy otherwise lost at the ends of the machine, lowering the fusion gain needed to make the economics work.

Furlong, Realta Fusion's CEO and co-founder, is not a plasma physicist by training. He is a chemical engineer with an MBA and a background in industrial and climate-tech commercialization, the kind of founder profile that matters in fusion because the sector's hard problem has shifted from lab physics alone to whether any design can be financed, built, maintained and sold into an energy market that does not pay extra for beautiful science. The physics spine of the company comes from UW-Madison researchers including Cary Forest, Realta Fusion's founding chief scientist, along with co-founders Jay Anderson, Ben Lindley and Oliver Schmitz, whose roles on the company site span plasma heating, blanket design and plasma-facing components.

What Realta Fusion actually showed

Realta Fusion mounted a prototype direct energy converter at one end of WHAM that uses electrostatic fields to slow charged particles and convert part of their kinetic energy into electrical current.

During mirror plasma operations, Realta Fusion said the assembly drew multiple amps of current at around 100 volts, enough to illuminate a few lightbulbs. TechCrunch quoted Furlong summing up the milestone in one sentence: "We can take power from a plasma."

That is the cleanest version of the news. The less marketable but more important version is that Realta Fusion is trying to turn a perceived weakness of magnetic mirrors into a product advantage.

Magnetic mirror machines confine plasma in a linear chamber using strong magnetic fields at both ends. Historically, the problem was that particles leak out of the ends too easily. Realta Fusion's argument is that modern high-temperature superconducting magnets improve confinement enough that the remaining leakage can be useful. If charged particles are going to exit through the machine's loss cone, a direct converter at the end of the device can try to harvest some of that energy instead of wasting it as heat.

For first-generation deuterium-tritium plants, Realta Fusion says about 80% of the fusion yield would come as high-energy neutrons and about 20% as charged helium nuclei, or alpha particles. The neutron energy still has to be captured as heat in a blanket and used directly for industrial process heat or converted into electricity through a turbine. The alpha-particle portion is the opening for direct conversion.

Furlong told TechCrunch he estimates direct conversion can be about 90% efficient, versus roughly one-third for steam turbines in today's fission plants. Those are company estimates, not demonstrated plant economics.

Why the timing matters

Realta Fusion is coming off a year in which it moved from physics milestone to financing milestone and back again. WHAM achieved first plasma in July 2024 at UW-Madison's Physical Sciences Lab in Stoughton, Wisconsin. The WHAM project page says the device uses 17-tesla high-temperature superconducting magnets and operates as a public-private partnership with Realta Fusion, a UW-Madison spinout that contributes the majority of current funding.

In May 2025, Realta Fusion announced a $36 million Series A led by Future Ventures, with participation from Mayfield, GSBackers, SiteGround, Avila VC, Khosla Ventures, Wisconsin Alumni Research Foundation and TitletownTech. The round was pitched to support plasma-physics validation, prototype engineering and facility planning.

The result also sharpens Realta Fusion's competitive story. Many private fusion companies sell a version of the same broad promise: carbon-free baseload power, enabled by magnets, lasers, pulsed power or new confinement geometries. Realta Fusion's narrower pitch is that its linear magnetic mirror architecture can be modular, factory-built and better matched to industrial heat and power customers than the megaproject model associated with large tokamaks.

That positioning has become more relevant as fusion startups push beyond physics credibility into siting, power-purchase agreements and plant economics. RuntimeWire has covered that split across the sector, including Focused Energy's $240 million Series A for laser fusion and Thea Energy's $100 million round for planar-magnet stellarators. Realta Fusion is smaller than those rounds, but the founder bet is similar: pick a hard technical path, show enough progress to make the next machine financeable, and avoid claiming the entire industry has been solved.

The commercial leap is still the story

Realta Fusion's own framing is unusually clear on what remains undone. The company says the WHAM demo was not net-electricity production and not large-scale conversion of fusion-born power. It now has to scale the direct converter from lightbulb-level output to multi-kilowatt and eventually multi-megawatt capability, while also proving the underlying reactor can sustain the plasma conditions required for a power plant.

That leaves the familiar fusion checklist: sustained operation, engineering gain, tritium handling and breeding, neutron damage, materials lifetime, plant availability, manufacturing cost, customer integration and regulatory execution. Direct conversion helps only if the rest of the machine works.

Still, it is a meaningful result because it targets the less glamorous question that decides whether fusion companies become energy companies: not whether a plasma can be made hot, but whether enough usable power can be extracted from the system at a cost customers will pay. Furlong's bet is that Realta Fusion can make the mirror's leakage part of the design rather than a fatal flaw. On June 19, Realta Fusion showed that idea can move current through a circuit. The next question is whether it can move the economics of a plant.