For fusion startups, the hard part is over: Thanks to a groundbreaking experiment in 2022, we know that controlled nuclear fusion reactions can generate more power than they consume. But now companies need to prove their reactors can make enough electricity to be profitable.

One option is to simply turn up the temperature, generating more heat to produce more steam to spin a bigger turbine. Another is to harvest electricity directly from the fusion reactions themselves, an approach that promises to be more efficient.

Realty Fusion announced that an experiment it conducted on June 19 successfully powered a lightbulb using electricity harvested directly from WHAM, its demonstration fusion device. The Wisconsin-based startup believes it is the first private company to publicly demonstrate such a feat.

“We can take power from a plasma,” Kieran Furlong, co-founder and CEO of Realta Fusion, told TechCrunch. The milestone shows “what’s possible,” he added.

Realta plans to use direct electricity conversion to heat the plasma in its reactor, a process that requires a lot of energy. Furlong estimates that direct conversion is about 90% efficient, meaning it will convert 90% of the potential energy into electricity. By comparison, steam turbines in today’s fission reactors are about 33% efficient. The more energy the company is able to harvest, the quicker it will get to profitability.

Every power plant consumes some of the power it produces simply to operate, and fusion reactors are no exception. The big challenge fusion startups face today is building reactors that can produce more energy than they consume. The efficiency boost from direct energy conversion should make clearing that hurdle easier.

About 20% of the energy from fusion reactions fueled by deuterium-tritium, the kind Realta plans to use in its commercial reactors, are charged helium nuclei known as alpha particles. The startup built a prototype electricity converter and attached it on the end of its reactor. There, it was able to harvest enough “alpha power” to generate multiple amps of electricity at 100 volts, powering a few lightbulbs.

On a commercial scale power plant, the direct energy converters should provide enough energy to heat the plasma. “You’re basically able to recirculate the electricity,” Furlong said. 

Ultimately, Furlong estimates that circularity could boost a commercial scale power plant’s total output by 20% to 30%. “Spinning a flywheel of electricity, if you like, is very beneficial,” he said.

Though it might be the first to demonstrate direct energy conversion, Realta isn’t the only startup planning to deploy that technology in its reactor. For Helion, the startup backed by Sam Altman, direct energy conversion is key to its plans, though it has yet to demonstrate it publicly.

Harvesting electricity directly from the fusion reaction “really helps with the economics” of a reactor’s design, Furlong said.

Realta previously raised $36 million in a Series A led by Future Ventures in 2025. Furlong said the company is in the midst of raising a new round.