As the race to commercialize controllable nuclear fusion enters the "proven profitable" stage, U.S. startup Realta Fusion announced that in an experiment on June 19, it successfully lit up a light bulb using electricity obtained directly from the fusion reaction. It believes this is the first time a private company has publicly demonstrated such results. "We can get electricity from plasma," company co-founder and CEO Kieran Furlong told TechCrunch, adding that the milestone shows "what might be possible in the future."
In the previous year of 2022, scientific research institutions have proved through landmark experiments that controllable nuclear fusion reactions can achieve "energy gain", that is, the output energy exceeds the input energy, making fusion move from theory to experimental reality. But at the commercial level, the real question has shifted from "can it be done?" to "can it generate electricity stably and cheaply enough?" As fusion start-ups of all kinds now have to prove that their reactors are economically viable.
Under the traditional concept, one of the ways to improve the power generation capacity of fusion power plants is to simply increase the plasma temperature, drive more steam through higher heat, and then drive larger steam turbines to generate electricity. The route taken by Realta is to "harvest electricity" directly from the fusion reaction itself, bypassing part of the thermal-mechanical conversion link. This solution is theoretically expected to significantly improve overall energy efficiency.
Furlong estimates that the direct energy conversion process used by Realta is about 90% efficient, which means that about 90% of the potential energy can be converted into electricity for the reactor itself or for external output. In comparison, the current thermoelectric conversion efficiency of steam turbines in many fission nuclear power plants is about 33%, and a large amount of energy is "wasted" in heat conduction and mechanical losses. Therefore, if direct conversion can be implemented on a large scale, it will form an important support for the economics of fusion power plants.
The experiment was completed by Realta on its demonstration device WHAM, which is designed to demonstrate the company's "magnetic mirror fusion" technology route. In the experiment, Realta tested energy recovery for a deuterium–tritium fuel configuration it plans to use in commercial reactors, in which about 20 percent of the energy of a fusion reaction is released in the form of charged helium nuclei (alpha particles). Realta installed a prototype power converter at the end of the reaction device and successfully collected multi-ampere, about 100 volts of current from these "alpha energy", which was enough to light up several light bulbs, thus completing a "closed-loop demonstration" from plasma to actual electricity use.
In larger-scale commercial power plants, Realta plans to use the direct energy conversion device mainly to supply energy for plasma heating in the reactor, reducing external power supply needs and achieving "recycling" of electricity. Furlong estimates that this power "loop" mechanism based on direct energy conversion is expected to increase the total output of commercial power stations by 20% to 30% as a whole, which is equivalent to providing a continuously "accelerating" power flywheel for fusion power stations.
Realta isn't the only fusion company betting on direct energy conversion, but it appears to be the first private company to publicly demonstrate this capability. Fusion company Helion, backed by Sam Altman, also counts direct energy conversion as one of its core technologies but has yet to demonstrate results in public experiments. Furlong points out that being able to collect electricity directly from fusion reactions "will greatly help the overall economics of the reactor" and is expected to be a key factor in determining which fusion routes will be commercialized first.
At the capital level, Realta completed a $36 million Series A round of financing led by Future Ventures as early as 2025 to promote the development and verification of its "fusion reactor in a bottle" solution. Furlong said that the company is currently preparing for a new round of financing and hopes to accelerate the progress of engineering verification and prototype power station construction while consolidating technological milestones.
Industry analysts believe that as more and more start-ups move from "lighting a light bulb" to "driving a unit or even a power station," the focus of competition for fusion power generation will gradually shift from pure technological breakthroughs to cost, reliability, regulatory paths, and supply chain construction. Although Realta's experiment is limited in scale, it is the first time that a private company has publicly demonstrated the ability to draw electricity directly from fusion plasma. It is still regarded as a symbolic node on the road to commercialization of fusion.