Thea Energy has submitted a comprehensive preconceptual design for Helios, a planar‑coil stellarator power plant, to the U.S. DOE, closing its initial DOE milestone. Helios is designed to deliver about 400 MW net electric (1.1 GW thermal) from a compact 8 m major‑radius architecture and targets >85% capacity factor with a >40‑year plant lifetime. Key innovations include software‑controlled planar coils, the first tokamak‑like X‑point divertor in a stellarator, and validated high‑fidelity simulations run on PPPL and DOE supercomputers.
Thea Energy Finalizes Helios Preconceptual Design for 400 MW Planar‑Coil Stellarator
Thea Energy, a 2022 spin‑out from the Princeton Plasma Physics Laboratory and Princeton University, has completed and submitted a comprehensive preconceptual design for its Helios stellarator power plant to the U.S. Department of Energy under the Milestone‑Based Fusion Development Program. The submission, announced on December 15, closes the company's initial set of DOE milestones and is accompanied by an initial technical paper titled "Overview of the Helios Design: A Practical Planar Coil Stellarator Fusion Power Plant," available as a preprint on Thea’s website and arXiv. The company has submitted the work and additional subsystem manuscripts for peer review.
Thea is reimagining the stellarator by combining planar, software‑controlled magnet coils with modern computation, real‑time controls and AI. Thea’s roadmap includes a near‑term demonstration system (Eos) intended to demonstrate steady‑state, power‑plant‑relevant fusion by about 2030, and the larger commercial Helios plant planned for operation in the 2030s.
Design Highlights and Innovations
- Power and Scale: Helios is designed to produce about 400 MW net electrical output with ~1.1 GW thermal output and a major radius of 8 meters, yielding one of the most compact optimized stellarator power‑plant footprints proposed.
- Planar, Programmable Coils: The architecture uses individually controllable planar coils governed by a software stack that can compensate for manufacturing tolerances, assembly errors and long‑term wear — and enable AI‑driven performance improvements over the plant lifetime.
- Tokamak‑Like X‑Point Divertor: For the first time in a stellarator power‑plant design, Helios incorporates a tokamak‑style X‑point divertor intended to simplify exhaust geometry and improve gas and heat removal — the company reports ~10× better exhaust effectiveness versus previous stellarator divertors.
- Maintainability and Lifetime: A sector‑based maintenance approach enabled by the planar coil layout allows removal of entire toroidal sectors with relatively few unique parts, targeting >40‑year plant lifetime and a capacity factor above 85%.
- Engineering Parameters: Helios design calls for superconducting coils with peak fields up to 20 T (consistent with large‑bore HTS magnet demonstrations), and radial build providing >1 m for blankets and shielding. First‑wall components are projected to have an average operational lifetime of ~15 years before replacement.
- Validated Simulations: High‑fidelity simulations run on PPPL and DOE NERSC resources assessed turbulent transport, fusion‑product confinement, MHD stability and plasma exhaust. Thea used advanced codes — including M3D‑C1 — and reports low turbulent transport and credible access to required operating conditions.
Comments and Next Steps
"Helios is designed to combine the inherent benefits of the stellarator — steady‑state operation, no risk of damaging disruptions, and high efficiency — with programmable, planar magnets," said David Gates, Ph.D., co‑founder and CTO of Thea Energy.
Brian Berzin, co‑founder and CEO, noted that the preconceptual design is catalyzing commercial partnerships and customer interest. Thea’s team now numbers over 80 engineers, scientists and commercialization experts. The company is in discussions with five U.S. states about siting Eos and expects to announce a location in 2026.
Independent experts and investors offered supportive commentary: Columbia University’s Carlos Paz‑Soldan highlighted the manufacturability and maintenance advantages of planar coils and praised the novel power‑handling topology; Scott Hsu of Lowercarbon Capital emphasized the architecture’s modularity and cost focus; and Jonathan Menard of PPPL noted the use of supercomputing resources and modern codes to simulate key plant performance metrics.
Thea views Helios as a practical, near‑term pathway to a maintainable, controllable stellarator power plant that does not rely on unspecified scientific breakthroughs. The company continues to refine subsystem designs and pursue peer review and commercialization steps as it progresses toward demonstration and commercial deployments.
