Fusion research company Helion Energy said its Polaris prototype has set new industry benchmarks, becoming the first privately developed fusion energy machine to demonstrate measurable deuterium-tritium (DT) fusion and achieve plasma temperatures of 150 million degrees Celsius.
The company on February 13 said the milestones “mark significant breakthroughs in Helion’s vision to make commercially viable fusion energy a reality and are firsts for the private fusion industry.”
Helion, based in Everett, Washington, was founded in 2013 and began operating its 7th-generation Polaris prototype in late 2024. The company said the milestones announced Friday were achieved in January of this year.
“We believe the surest path to commercializing fusion is building, learning and iterating as quickly as possible,” said David Kirtley, co-founder and CEO of Helion. “We’ve built and operated seven prototypes, setting and exceeding more ambitious technical and engineering goals each time. The historic results from our deuterium-tritium testing campaign on Polaris validate our approach to developing high power fusion and the excellence of our engineering.”
Kirtley told POWER, “With Polaris, we’ve crossed two critical thresholds. We operated with deuterium-tritium fuel and reached plasma temperatures over 150 million degrees Celsius. These are important steps on the road to Orion,” which is planned as Helion’s first commercial power plant. “We’re focused on turning fusion reactions into electricity and getting reliable power onto the grid by 2028.”
Kirtley added, “Our philosophy has always been to build, test, iterate, and repeat as fast as possible. And that’s exactly what we’re doing right now. Polaris is running nearly every day, validating our approach to recovering electricity and refining the technology we’ll use to build Orion and the many fusion power plants that will follow.”
Among Several Groups Working on Fusion
Helion is among several companies featured in POWER’s “Groundbreakers” Special Report published this month. The report provides information about fusion energy and other power generation technologies and facilities that are being developed to support the electricity sector. Helion has hit several benchmarks over the past few years, including being the first company to receive regulatory approval to possess and use tritium for the purpose of demonstrating fusion energy production. Achieving thermonuclear fusion using DT fuel is one step in Polaris’ testing program. The company has said it will continue testing to reach optimal temperatures for deuterium-helium-3 fusion, a fuel Helion will use for commercial operations. (Editor’s note: Helium-3 is a light, stable isotope of helium with two protons and one neutron. The most common isotope, helium-4, has two protons and two neutrons.)
In achieving plasma temperatures of 150MºC in Polaris, Helion broke its own commercial fusion industry record for plasma temperatures of 100MºC, which was set by its 6th-generation Trenta prototype. Helion ended operation of Trenta in 2023. Within the fusion industry, 100MºC is considered the threshold plasma temperature for a commercially relevant fusion machine. Helion has said it will continue to increase plasma temperatures in its Polaris machine to demonstrate that it can reliably operate with deuterium-helium-3, which will be relevant for future Helion commercial operations.
“I had the opportunity to review diagnostic data from Helion,” said Ryan McBride, an expert in inertial confinement fusion, pulsed power, and plasma physics. McBride has experience as a department manager at Sandia National Laboratories, and as a professor of nuclear engineering, electrical engineering, and applied physics at the University of Michigan. “It is exciting to see evidence of DT fusion and temperatures exceeding 13 keV or 150 million degrees Celsius, and I look forward to seeing more progress.”
Agreements with Microsoft, Nucor
Helion in July 2025 began construction at the site of Orion, the company’s first commercial machine, in Malaga, Washington. That project is being built to deliver electricity from fusion to the grid for technology giant Microsoft. The company also has an agreement with Nucor, a manufacturer of steel and steel products, as part of a collaboration to develop a 500-MW fusion power plant to supply baseload electricity to a steelmaking facility.
“While the path to commercial fusion is still unfolding, we’re proud to support Helion’s pioneering work here in Washington state as part of our broader commitment to investing in sustainable energy,” said Melanie Nakagawa, Microsoft’s chief sustainability officer, when ground was broken at the Orion site in July of last year.
“I am impressed with our nation’s ingenuity and the pace at which we are de-risking our path to fusion commercialization,” said Jean Paul Allain, associate director of Science for Fusion Energy Sciences in the Department of Energy’s Office of Science. “Seeing the data from the Polaris test campaign, including record-setting temperatures and gains from the fuel mix in their system, indicates strong progress. Our ability to get fusion on the grid requires approaches that enable rapid turnaround in design and testing, and these results reflect the growing capability of the U.S. fusion ecosystem.”
—Darrell Proctor is a senior editor for POWER.
