The U.S. Department of Energy has certified Thea Energy's preconceptual "Helios" pilot plant design following a comprehensive review by independent fusion experts from national laboratories, research institutions, and universities. The certification makes the New Jersey-based stellarator developer the first awardee in the DOE's Milestone-Based Fusion Development Program to complete its final major design milestone, validating both the physics basis and engineering feasibility of putting fusion power on the grid.

"This final design milestone, now certified by the DOE, substantiates the validity of the planar coil stellarator and shows a clear pathway to a deployable power plant," said Brian Berzin, co-founder and CEO of Thea Energy.

DOE reviewers conducted an on-site visit to Thea Energy's Kearny headquarters and evaluated a 200-page technical report detailing the Helios design.

Read the press release from Thea Energy here. 

What the DOE Actually Validated

The Helios design introduces several capabilities previously undemonstrated in fusion systems. 

DOE reviewers specifically certified:

• Software-controlled magnet coils that dynamically adapt to real-world operating conditions, a departure from the fixed-geometry magnets used in traditional stellarator designs.
• A stellarator divertor exhaust system engineered for sustained fusion power operations, addressing one of the key engineering challenges for continuous-operation fusion devices.
• Sector-based maintenance architecture designed for long-term commercial plant viability, allowing components to be serviced without complete reactor disassembly.

Princeton Plasma Physics Laboratory professor Felix Parra-Diaz, who served on the expert review committee, noted the level of technical rigor in the submission. "Helios represents a new era for the stellarator where this magnet array and plant design pushes fusion towards a commercial format," he said. "I had the chance to dive deep into Thea Energy's Helios plant and verify that the Company had executed on this design with a remarkable degree of technical detail and high standards."

The company has published an overview paper on arXiv and submitted additional technical manuscripts to peer-reviewed journals.

Stellarator Technology Gains Traction

Thea Energy's validation arrives as stellarator technology attracts increasing private investment. The twisted magnetic bottle design, pioneered by Lyman Spitzer at Princeton in the 1950s, has historically received less commercial attention than tokamaks despite strong theoretical advantages for continuous operation. Stellarators can maintain plasma indefinitely without the pulsed current requirements of tokamaks, a characteristic that simplifies the engineering path to steady-state power generation.

That funding gap is beginning to close:

• Proxima Fusion: raised €130 million in Series A funding in May 2025 for its stellarator program in Munich.
• Type One Energy: secured an additional $87 million via convertible note this week, bringing total funding past $160 million. The company has signed agreements with Tennessee Valley Authority to site its first commercial plant, called Infinity Two, at a former coal facility in Tennessee, targeting 350 MW output by the mid-2030s.
• Thea Energy: now holds the distinction of having the first DOE-validated commercial stellarator pilot plant design. The company has raised over $30 million in private funding, including a $20 million Series A led by Prelude Ventures in early 2024, and receives additional non-dilutive funding through DOE programs including six INFUSE awards supporting collaboration with national laboratories.

Position Within the Milestone Program

The DOE's Milestone-Based Fusion Development Program was modeled after NASA's Commercial Orbital Transportation Services initiative, the pay-for-performance structure credited with catalyzing the private space industry. Eight companies were selected in May 2023: Commonwealth Fusion Systems, Focused Energy, Princeton Stellarators (now Thea Energy), Realta Fusion, Tokamak Energy, Type One Energy, Xcimer Energy, and Zap Energy.

All eight awardees have been working toward presenting preconceptual designs and technology roadmaps within the first 18 months of the program. Thea Energy is the first among them to receive DOE certification of its complete pilot plant design.

Other awardees have completed earlier milestones. Focused Energy produced computational modeling for its laser-driven inertial fusion target design and demonstrated ion beam focusing. Realta Fusion completed whole-device modeling of simple mirror equilibria. Commonwealth Fusion Systems received validation for manufacturing and testing a production toroidal field magnet.

The program requires companies to provide more than 50% of milestone costs, with DOE validation serving as a credibility signal for subsequent fundraising. Milestone awardees have collectively raised over $350 million in new private funding since selection, compared to $46 million in federal funding initially committed.

Path to Commercialization

Thea Energy plans to operate Helios in the 2030s. The pilot plant will follow "Eos," a large-scale demonstration system designed to achieve power-plant-relevant, steady-state fusion by 2030. The company is currently evaluating five states for the Eos facility and expects to announce its site selection this year.

The Helios certification positions Thea Energy to proceed into the next phase of the Milestone Program, where awardees plan to build and operate major integrated experiments and demonstrate critical underlying technologies for their pilot plants. Continued progress remains contingent on Congressional appropriations and successful negotiation of future milestones.

Commercial Interest in Fusion Power

The timing of Thea Energy's validation coincides with growing corporate interest in fusion as a potential power source. Google signed a 200 MW power purchase agreement with Commonwealth Fusion Systems in June 2025, the largest direct corporate offtake agreement for fusion energy. Microsoft's 2023 agreement with Helion Energy established an earlier template for technology companies committing to future fusion power.

Berzin noted that the DOE certification "allows us to definitively communicate confidence in this design to the interested power offtakers and hyperscalers that we are in conversations with." He expanded on Thea Energy's commercial strategy and technical approach at The Fusion Report's Fusion 2035: The 10-Year Shot Clock webinar earlier this year.

With over $9.8 billion in private capital now deployed across the fusion sector, validated pilot plant designs represent tangible progress toward the commercial deployment that investors and potential customers are evaluating.