Private fusion's year of firsts: Helion hits 150M°C on D-T, Realta converts plasma to power

Helion Energy says its seventh-generation Polaris prototype is the first privately developed fusion machine to demonstrate measurable deuterium-tritium (D-T) fusion, and the first to hit plasma temperatures of 150 million degrees Celsius (MºC). The Everett, Washington company announced both results on 13 February 2026 and called them industry firsts. Polaris began operating at the end of 2024, and this January it became the first and currently only private fusion machine to run on D-T fuel.

The temperature figure broke Helion's own record of 100MºC, set by its sixth-generation Trenta prototype. Inside the fusion industry, 100MºC is treated as the threshold plasma temperature for a commercially relevant machine. Helion says it will keep pushing Polaris temperatures higher to show reliable operation on deuterium-helium-3, the fuel it intends to use in commercial plants.

What the D-T campaign actually proves

Running on D-T is not the endpoint for Helion, but it is a hard engineering test. The company says it was the first to win regulatory approval to possess and use tritium for demonstrating fusion energy production, and that the D-T campaign shows it can operate and scale across multiple fuels. The results drew comment from outside the company. Jean Paul Allain, Associate Director for Fusion Energy Sciences at the Department of Energy's Office of Science, said he was impressed with the pace of de-risking and that the data indicated strong progress. Ryan McBride, an inertial confinement fusion and pulsed power expert, said he had reviewed diagnostic data and called the evidence of D-T fusion and temperatures above 13 keV, or 150MºC, exciting.

"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.

Fusion is not yet a grid product. In July 2025, Helion began construction on the site of Orion, its first commercial machine, in Malaga, Washington.

The company says Orion will deliver electricity from fusion to the grid for Microsoft. That is a build milestone, not a power milestone, and Helion's own framing puts plenty of testing between the Polaris results and commercial operation. The D-T campaign is one step in the Polaris testing program, not its conclusion.

A different first, from a different machine

Five months after Helion's announcement, Realta Fusion reported a first of a different kind. On 19 June 2026, working with the University of Wisconsin-Madison on the Wisconsin HTS Axisymmetric Mirror (WHAM) device, the company demonstrated direct energy conversion (DEC) of plasma kinetic energy into electricity. Realta says this was the first time a commercial fusion company has demonstrated DEC applied to a fusion plasma. DEC captures the energy of charged particles leaving the plasma directly as electric current, instead of routing all of it through a thermal cycle with its built-in efficiency limits.

The prototype is modest by design. A single-stage converter sits on the end-ring assembly in place of the center disk and uses three finely meshed grids: a grounded grid, an electron repulsion grid and an ion collector grid. Realta says the assembly draws multiple amps of current at around 100 volts, enough to light a few lightbulbs. The company plans to raise the converter voltage to draw more current in the coming weeks. It is also explicit about what the demo does not show: no net electricity production and no large-scale conversion of fusion-born power. WHAM runs on deuterium only, so most of the converted energy came from input power supplied to heat and sustain the plasma.

Money keeps moving toward the grid

The technical results sit inside a funding cycle that has not slowed. Thea Energy, a stellarator company spun out of Princeton University and the Princeton Plasma Physics Laboratory in 2022, announced a $100 million Series B on 27 May 2026. Thomas Tull's US Innovative Technology Fund led the round, with participation from General Innovation Capital Partners, Linse Capital and a longer list of investors including Idemitsu Kosan. Thea says the money will expand magnet manufacturing, including a second facility in Northern New Jersey, and support siting and construction of Eos, a large-scale integrated stellarator. The company says it plans to pick a site for Eos later this year and to double its team.

Thea's pitch rests on its magnet architecture. Gaetano Crupi, a managing director at USIT, said the stellarator is inherently stable, but that earlier 3D stellarator magnets made the system impractical to build, and that Thea shifts complexity from precision mechanical fabrication to software-defined controls. The company says it has built and operated the first superconducting magnet array capable of producing the complex fields commercial stellarators need. It also holds a Department of Energy certification of its Helios preconceptual design milestone, which it says it was the first awardee to receive.

The public project in the middle

Private milestones are arriving while ITER, the publicly funded international reactor in southern France, works through a difficult stretch. CNET reported in May 2026 that the project carries an estimated cost of $22 billion. Cracks found in 2020 in the piping of a heat shield, along with welding distortions and COVID-19 disruption, pushed the timeline back by years and required an additional $5 billion for repairs. The machine is designed to contain 150-million-degree plasma using superconducting magnets kept just a few degrees above absolute zero, with only a thin heat shield between the hottest and coldest environments. That is the same temperature figure Helion now claims for Polaris, in a machine a fraction of the size and cost.

The comparison is not straightforward.

ITER is built to answer physics and engineering questions at a scale no private company is attempting, and its results are shared among more than 30 member countries. Javier Artola, a scientist modelling ITER's plasma behaviour, told CNET the project is publicly funded and belongs to the knowledge of the world. Laban Coblentz, ITER's chief strategic advisor, framed the collaboration itself as the achievement: countries of unlike persuasion working together for decades.

For all the momentum, the near-term scoreboard is mixed. Helion's 150MºC is a temperature record, not a power record. Realta's converter lit a few lightbulbs and ran mostly on input power. Thea's power plant is targeted for before the end of the decade. Thea says it is in talks with more than a dozen power offtakers, hyperscalers and utility partners, which signals demand rather than delivery.

What changed in 2026 is narrower and more concrete than the usual fusion optimism. A private machine ran on the fuel that produces the most neutrons, and another turned escaping charged particles into measurable current. Both are steps on a long path, and both companies say so. The next test is whether those steps scale into devices that produce more than they consume.