US-based Thea Energy Unveils Helios Stellarator Fusion Power Plant Design

On September 9, 2026, Thea Energy, Inc., a fusion energy company based in Kearny, New Jersey, announced that 16 peer-reviewed papers on its "Helios" fusion power plant design had been published in a special issue of Fusion Engineering and Design (FED). The special issue, titled "Thea Energy's Helios Stellarator Power Plant Design," presents the Helios architecture and its key engineering solutions.

According to Thea Energy, Helios is a stellarator fusion power plant architecture oriented toward commercial deployment requirements, integrating magnet coils that can be controlled by software to adapt to actual operating conditions, a stellarator divertor exhaust system for continuous fusion power generation operations, and a sectorized maintenance scheme supporting long-term operation. The company states that Helios aims to continuously deliver approximately 400 megawatts of electricity to the grid and to avoid plasma disruption risks.

David Gates, co-founder and Chief Technology Officer of Thea Energy, said that Helios adopts a planar coil stellarator approach intended to address the engineering challenges posed by the complex three-dimensional modular coils of conventional stellarators. He said the design can maintain operation while accounting for manufacturing deviations and operational wear, which is an important condition for fusion power plants to achieve cost competitiveness and commercialization.

The pre-conceptual design of Helios had previously been certified through the first phase of the US Department of Energy (DOE) "Milestone-Based Fusion Development Program." Thea Energy states that it is the first awardee in the program to receive power plant design milestone certification, with the relevant certification completed through review by an independent panel of fusion experts. The company plans to advance Helios to operation in the 2030s; prior to that, its first large integrated stellarator device, "Eos," will be brought into service first. Eos adopts the same planar coil stellarator architecture as Helios and will validate power plant-relevant fusion performance.

Benedikt Geiger, an associate professor at the University of Wisconsin-Madison who served as a guest editor for the special issue, said that the approach proposed by the Thea Energy team covers key subsystems including remote operations, heat transfer, cryogenics, power supplies, diagnostics and instrumentation and control, and planar coil magnet engineering. Among these, the use of planar coils and the introduction of an "X-point" divertor are considered helpful in reducing engineering complexity in stellarator fusion power plant design.

Sophia Henneberg, an assistant professor in the Department of Nuclear Science and Engineering at MIT, said that the stellarator is a mature magnetic confinement fusion technology pathway, but complex coil geometry has long constrained engineering options. She believes that this FED special issue systematically presents the Helios pre-conceptual design and is one of the cases in the private fusion sector in which research results have been submitted for rigorous peer review.

According to design highlights disclosed by Thea Energy, Helios has a major radius of 8 meters and adopts a quasi-axisymmetric design and a relatively simplified hardware scheme. The company states that this helps reduce the device footprint and cost. Helios also adopts a sectorized maintenance approach, in which entire toroidal sectors can be removed radially, with a target capacity factor exceeding 85% and a system lifetime exceeding 40 years.

Regarding core and component lifetime, the Helios design maintains a distance of 1.2 meters between the fusion plasma and the magnetic coils to accommodate the blanket and shielding. Thea Energy states that this design helps improve component lifetime. Neutronics analysis shows that its first wall system has a minimum lifetime of 11 years and an average lifetime of 18 years. Helios will use known materials to manufacture plasma-facing components and will adopt deuterium-tritium fusion technology.

Helios will also introduce an X-point divertor similar to that in tokamak devices into the stellarator power plant architecture. Thea Energy states that this divertor geometry is relatively simple and has higher exhaust efficiency than previous stellarator divertor schemes. The company also states that Helios does not rely on future scientific breakthroughs, and its superconducting coils have a maximum magnetic field of 20 tesla, which is within the engineering parameter range already achieved by large-bore high-temperature superconducting magnets.

Thea Energy was founded in 2022, spun out from projects related to Princeton University and the Princeton Plasma Physics Laboratory, and focuses on advancing the commercialization of the planar coil stellarator architecture. The company has been selected among the first batch of awardees in the US Department of Energy "Milestone-Based Fusion Development Program" and has received support from six DOE INFUSE awards and one ARPA-E SCALEUP award.