What is a stellarator?

How it works

The U.S. Department of Energy (DOE) describes a stellarator as a machine that uses magnetic fields to confine plasma in a doughnut shape called a torus. Another design, the tokamak, induces an electric current inside the plasma to help control it. A stellarator generates its twisting field with external coils instead.

DOE lists the advantages as less injected power to sustain the plasma, more design flexibility and simpler plasma control in some respects. It names coil manufacturing as a challenge demanding millimeter precision. The Max Planck Institute for Plasma Physics (IPP) describes continuous operation as the essential property of the design. It says this avoids the disadvantages of a tokamak's large plasma current.

Where it came from

DOE says Lyman Spitzer invented the concept at Princeton University in 1951. It says much early work in the 1950s happened at what is now its Princeton Plasma Physics Laboratory.

Where things stand in 2026

Wendelstein 7-X in Greifswald, Germany, which IPP calls the world's largest stellarator, produced its first plasma on December 10, 2015. IPP reported that on May 22, 2025, the machine sustained a new peak value of the triple product for 43 seconds. It said this beat tokamaks at longer plasma durations. The triple product multiplies plasma density, temperature and energy confinement time. IPP calls it the key metric on the path to a power plant. A June 30, 2025, update added that if then-unpublished results from the decommissioned JET tokamak were counted, the two machines were joint leaders. IPP said in July 2026 that the machine reached an 8-minute plasma in 2023. It said 30 minutes is the target for the coming years.

Companies are also pursuing the design. IPP said on July 8, 2026 that Proxima Fusion, its first spin-out, had completed a 411 million euro funding round. It called this a milestone for Alpha, a demonstration stellarator planned near IPP's Garching site. It added that 1.2 billion euros of federal funding, also required, had not then been committed.

Tennessee's Department of Environment and Conservation announced on August 31, 2026 that it had issued Type One Energy the state's first fusion-specific byproduct material license. Nuclear Newswire reported that the company plans a prototype, Infinity One, at the Tennessee Valley Authority's Bull Run site. It said a 400-megawatt pilot plant would follow, which the company expects to start up fully by 2034.