France Is Developing an Alternative to ITER in Nuclear Fusion: A Commercial Stellarator Reactor

Experimental stellarator reactors offer a viable alternative to tokamak reactors, such as the International Thermonuclear Experimental Reactor (ITER) and the Joint European Torus (JET). Both designs originated in the 1950s. American physicist Lyman Spitzer developed the stellarator as a foundation for Princeton University’s Plasma Physics Laboratory.

Soviet physicists Igor Yevgenyevich Tamm and Andrei Dmitrievich Sakharov created the tokamak, building on ideas proposed a few years earlier by their colleague Oleg Lavrentyev. Both designs aim to confine plasma at extremely high temperatures. In the 1950s and 1960s, the stellarator gained strong support from the Western scientific community due to its perceived potential.

However, when Soviet and American scientists later published comparative results, they found that tokamaks outperformed stellarators by one or two orders of magnitude. From then on, scientists largely shifted focus to the tokamak design. The primary difference between the two designs lies in their geometry, though further examination reveals that stellarators still have significant potential.

Renaissance Fusion’s Commercial Plans for Stellarators

Tokamak reactors are toroidal (doughnut-shaped), while stellarators feature a more complex geometry, resembling a twisted doughnut. The key difference, however, is in how they generate the magnetic fields to confine plasma. In tokamak reactors, magnetic fields are created with coils and induced by the plasma itself. In stellarators, the fields are generated entirely by coils, eliminating the need for plasma-induced current. This design makes stellarators more complex and challenging to construct.

Despite this complexity, French company Renaissance Fusion plans to commercialize power plants using a stellarator-type fusion reactor, according to Innovation News Network. Both tokamaks and stellarators are magnetic confinement fusion reactors, meaning they trap plasma—a superheated gas containing fuel—in an intense magnetic field.

The magnets responsible for generating the magnetic field are crucial to Renaissance Fusion’s design. The company claims that its engineers have simplified the stellarator reactor to make it viable for commercial power plants in the medium term. Its strategy involves the use of high-temperature superconducting magnets and liquid metal shields. However, according to the developers, the difference is that their machine is more efficient than other reactors based on magnetic confinement.

Renaissance Fusion says its high-temperature superconducting magnets are four times more potent than other experimental fusion power reactors. This allows it to reduce plasma volume by a factor of 256, increasing the fusion rate. The company also plans to coat the vacuum chamber walls with lithium, which absorbs 99.99% of the fast neutron energy from the fusion reaction. This design prevents the steel walls from becoming activated and radioactive.

The growing number of projects focused on making fusion energy a reality is promising. However, Renaissance Fusion has yet to announce when it expects to complete the first prototype of its stellarator reactor or to begin building a commercial power plant. The company has pledged that its technology will be ready in time to address the climate crisis driven by greenhouse gas emissions. Time will tell if it can fulfill this promise.

Image | Oak Ridge National Laboratory (ITER)

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