Helion reports first private D-T fusion plasma and 150 million degree milestone

The Everett, Washington company said Polaris, its seventh-generation prototype, hit both marks during a testing campaign that began in January. Helion's announcement says the machine started operating at the end of 2024.

Mainstream fusion projects have chased D-T fusion for decades because it ignites at lower temperatures than most alternatives. Helion says the campaign showed the machine can run on multiple fuels. The company also says it was the first to win regulatory approval to possess and use tritium for demonstrating fusion energy production.

"We believe the surest path to commercializing fusion is building, learning and iterating as quickly as possible," David Kirtley, Helion co-founder and CEO, said in the announcement. "We've built and operated seven prototypes, setting and exceeding more ambitious technical and engineering goals each time."

Two outside researchers reviewed diagnostic data for the company and are quoted in the release. Ryan McBride, an inertial confinement fusion and pulsed power specialist who has worked at Sandia National Laboratories and the University of Michigan, said he saw "evidence of D-T fusion and temperatures exceeding 13 keV or 150 million degrees Celsius." Alan Hoffman has more than 40 years of experience on field-reversed configuration plasmas and led early FRC work at the University of Washington. He said he continues to see the technology scaling.

The 150 million figure breaks Helion's own record of 100 million degrees Celsius, set by its sixth-generation Trenta prototype. The industry treats 100 million degrees Celsius as the threshold for a commercially relevant machine.

Jean Paul Allain, associate director for Fusion Energy Sciences at the Department of Energy's Office of Science, called the results "strong progress" in the same release. "Our ability to get fusion on the grid requires approaches that enable rapid turnaround in design and testing," he said.

None of this is a power plant result. D-T is a stepping stone in the Polaris test program. Helion says it will keep raising temperatures to show it can reliably run on deuterium-helium-3, the fuel it intends to use commercially. A company statement about the milestone is not the same as independent, peer-reviewed measurement, and Helion has not published the full diagnostic dataset.

Helion began construction in July 2025 at the site of Orion, its first commercial machine, in Malaga, Washington. That plant is meant to deliver fusion electricity to the grid for Microsoft. The company has not said when Orion will be finished or what it will cost.

The announcement comes as private fusion companies push against a much larger publicly funded project. ITER, the international tokamak under construction in southern France, is estimated to cost $22 billion, according to CNET, and is designed to contain plasma at 150 million degrees Celsius. Cracks found in the piping of its heat shield in 2020, along with welding distortions and COVID-19 disruptions, pushed back the schedule and added $5 billion in repair costs, CNET reported.

Javier Artola, a scientist modeling ITER's plasma behavior, told CNET the project is open: "This is a publicly funded project. It is the knowledge of the world." ITER's chief strategic advisor, Laban Coblentz, framed the collaboration of China, Russia, the US, Europe, Korea, India and Japan as "either genius or insane."

Private money keeps moving into the sector. Thea Energy, a stellarator company spun out of Princeton University and Princeton Plasma Physics Laboratory in 2022, said on 27 May 2026 that it raised $100 million in Series B funding led by USIT, with General Innovation Capital Partners and Linse Capital among the participants. The company said the money will expand magnet manufacturing, including a second facility in northern New Jersey, and support siting and construction of Eos, a large integrated stellarator.

Thea says it is the first awardee to receive Department of Energy certification of its Helios preconceptual design milestone under the Milestone-Based Fusion Development Program. It aims to start building the first Helios power plant before the end of the decade and says it is in talks with more than a dozen potential power offtakers, hyperscalers and utilities.

Other approaches are reporting their own firsts. Realta Fusion said that on 19 June 2026, with the University of Wisconsin-Madison, it became the first private fusion company to demonstrate direct energy conversion of plasma kinetic energy into electricity, on the WHAM mirror device. The single-stage converter drew multiple amps at around 100 volts, enough to light a few bulbs. Realta was explicit that this is neither net electricity production nor large-scale conversion of fusion-born power.

Helion's numbers are a data point, not an ending. The company still has to show D-He3 operation, and it still has to build the machine that sells power.