In the novel "The Three-Body Problem," interstellar spacecraft are powered by nuclear fusion energy, allowing us to envision a "picture of the future" and also to see the mission of nuclear fusion to provide unlimited clean energy for humanity.

In the process of promoting the development of nuclear fusion into a commercial power plant, engineers face a "dilemma."

Either choose a simple design and then force the plasma to keep running during operation to prevent it from extinguishing itself; or choose a complex design that is quite challenging but can produce a more ideal plasma.

Among the complex designs of magnetic confinement nuclear fusion, the stellarator is quite representative. It is an experimental device aimed at simulating a star.

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In 1951, the famous physicist and founder of the Princeton Plasma Physics Laboratory (PPPL, Princeton Plasma Physics Laboratory) in the United States, Lyman Spitzer, first proposed the concept of the stellarator.At that time, many people believed that this design was too complex, and the technological level of the mid-20th century was not sufficient to overcome the related challenges. Today, with the continuous advancement of superconducting materials and other new materials, scientists are beginning to rethink the possibility of making the stellarator a reality.

In a tokamak, a toroidal magnetic field is used to maintain the stability of the plasma. The strong magnetic field effectively controls the overheated plasma, preventing it from coming into contact with the reactor walls, thereby ensuring the stability and continuous progress of the fusion reaction.

Similar to the tokamak, the stellarator also uses magnetic fields to control the overheated plasma. The difference is that the stellarator usually has a twisted spiral shape, similar to a spiral or twisted "doughnut." Based on this design, its magnetic field is very complex, and the magnetic field lines need to follow a complex spiral path.

In 1983, with the introduction of the quasi-symmetry concept by PPPL physicist Allen Boozer, there was a significant shift in the theoretical understanding of the stellarator. This new paradigm made it theoretically possible to design a stellarator with confinement characteristics similar to those of a tokamak.

The stellarator has several key advantages, such as improving the stability of the reactor and maintaining the superheated gas inside it sufficiently stable. For future nuclear fusion power plants, the stellarator can theoretically operate continuously, while the tokamak must be stopped periodically to reset the magnetic coils.From the perspective of industrial development, companies that use stellarators as nuclear fusion reactors include: France's Renaissance Fusion, the United States' Type One Energy, Thea Energy, and Germany's Proxima Fusion, among others.

In 2015, researchers from the Max Planck Institute for Plasma Physics in Germany successfully manufactured the world's largest stellarator, Wendelstein 7-X (referred to as W7-X).

In 2018, W7-X demonstrated the feasibility of optimized stellarators through experiments, making it the first large-scale stellarator device and giving it an advantage in competition with tokamaks.

In 2023, Proxima Fusion became independent from the Max Planck Institute for Plasma Physics and completed seed round financing of more than 20 million US dollars.

Another startup company derived from a renowned fusion laboratory is Thea Energy.Based on the achievements in nuclear fusion technology by Princeton University in the United States and PPPL over the years, former PPPL physicist David Gates established Thea Energy in 2022, where he serves as the co-founder and CTO of the company.

The predecessor of Thea Energy was named Princeton Stellarators, aiming to utilize the latest breakthroughs in the field of stellarator physics and engineering to create a faster and simpler method for the commercialization of fusion energy.

It is important to understand that the three-dimensional complexity of the stellarator means that powerful computing capabilities are needed to fully master it.

Based on the current progress and development of computing and control systems, Thea Energy uses a planar and individually controllable array of electromagnetic coils, by transferring the complex 3D magnetic field to modern electronic control systems, this is a fundamentally new model that simplifies the stellarator system and can reduce costs.

Thea Energy's co-founder and CEO, Brian Berzin, said to the media: "Our technology simplifies the design of the stellarator by replacing the complex 3D magnetic coil, known for its complexity and high cost, with a more manageable array of small magnets."In May 2023, the U.S. Department of Energy launched a project called the "Milestone Fusion Development Program" and allocated $46 million to rapidly advance the development of commercial fusion energy.

Thea Energy, as one of the eight companies, was selected for this development program (named Princeton Stellarators at the time of selection).

In the selected project, Thea Energy is collaborating with the University of California, San Diego, to develop a renewable first wall based on the element boron (the vacuum chamber wall of the reactor), which can fully remove heat from the stellarator fusion device and recover tritium.

In February of this year, Thea Energy completed its Series A financing, raising $20 million.

Prelude Ventures led the round of financing, with other participating institutions including: 11.2 Capital, Anglo American, Hitachi Ventures, Lowercarbon Capital, Mercator Partners, Orion Industrial Ventures, and Starlight Ventures.According to public information, the funds raised in this round are used to support the construction and operation of Thea Energy's proprietary superconducting flat coil magnet array system, the design and simulation of the large-scale integrated neutron source stellarator system Eos, as well as the continuous development of the team.

Eos is a neutron source stellarator system capable of commercial operation, used for the production of various isotopes, including tritium.

According to Thea Energy's plan, the company intends to build a pilot reactor by the end of the 21st century and, before 2040, build a larger-scale 350-megawatt demonstration power plant. When its commercial products are connected to the power grid, Thea Energy hopes to achieve a power generation price of $50 per megawatt-hour.

In terms of financing progress of other companies using stellarators as nuclear fusion reactors, in July of this year, Type One Energy completed a new round of financing of more than 50 million US dollars, accumulating more than 85 million US dollars in seed financing.

There are still many challenges in promoting the full commercialization of stellarators, but the optimization and technological progress of stellarators may provide a "both can be achieved" solution for the "dilemma" of developing fusion energy into a commercial power plant.