There is a myriad of magnetic confinement solutions for fusion, each with its strengths and weaknesses
This week, The Fusion Report jumps into our third article in our “The Fusion Decathlon” series, where we are going to explore magnetic fusion energy (MFE; also known as magnetic confinement fusion, or MCF) solutions. If MFE companies were a group of runners, then they would be everything from sprinters, hurdlers, and 1.6 kilometer runners (also known as “milers”), all the way to marathon runners. Similarly, MFE solutions come in a variety of sizes, types and capabilities, including tokomaks (of which there are various flavors), stellarators, Z-pinch machines, field-reversed configurations (FRCs), and magnetic mirrors, just to name a few. Let’s dive into MFE solutions.
Tokamaks: The (Experimental) Grand-Daddy of MFE Solutions
Tokamaks are now over 75 years old, with the first tokamak (and first MFE) concept was proposed in 1950 by Soviet scientists Andrei Sakharov and Igor Tamm. The first functional MFE machine was a tokamak that was known as the T-1, a Soviet machine that was built in 1958. Since then, tokamaks have come a very long way. The current record of fusion power generated by a MFE device is held by the Joint European Torus (JET), which in 2021 sustained a gain factor of Q = 0.33 for 5 seconds, and which produced 59 megajoules of energy.
Tokamaks are donut-shaped devices, which combine a central solenoid with toroidal and poloidal magnets to shape a ring of plasma. The plasma is heated by a number of approaches such as neutral-beam injection, electron and ion cyclotron resonance, and lower hybrid resonance. As successive generations of tokamaks have been engineered, new problems regarding plasma stability have been encountered, forcing tokamak designs to become more complex. On the plus side, the invention of high-temperature superconductor (HTS) magnets enabled smaller tokamak designs, reducing their overall cost.
Tokamaks have several contenders in the Fusion Decathlon games. The largest tokamak proposed today is the International Thermonuclear Experimental Reactor (ITER), an experimental device being built in France and scheduled to be fully operational by 2039. ITER is the world’s largest fusion device, standing 30 meters tall and 30 meters wide. The device has a total weight 23,000 metric tons, and a plasma volume of 830 to 840 cubic meters. Unfortunately, ITER is also one of the most expensive fusion devices built to date, with a cost expected to exceed €20 billion. Most importantly, ITER does not have HTS magnets, which is the reason for its massive size, weight, and cost.
Arguably, the most advanced tokamak in operation today is the Commonwealth Fusion Systems (CFS) “Smallest Possible Affordable, Robust, Compact” (SPARC) tokamak, which is expected to achieve energy gain in late 2026. Unlike ITER, Spark is only 3 meters across; however, its HTS magnets are expected to be able to create a magnetic field of 12.2 Tesla. CFS expects that because of this, SPARC will be able to produce a thermal net energy gain of 140 MW. SPARC will be followed by CFS’s “Affordable, Robust, Compact” (ARC) tokamak in the early 2030s, which will be a fully functional electric power plant.
Stellarators: Magnetic Fusion With A Twist
If tokamaks are the granddaddy of magnet fusion, then stellarators are their (only slightly younger) brother. Proposed just a year later than tokamaks in 1951, stellarators use complex, twisted magnets that eliminate many of the issues with plasma instability that tokamaks had. While tokamaks rely on a large, induced current within the plasma to create the necessary helical magnetic fields, Stellarators use their physical twist to create a twist in the magnetic lines of the fields. Because there is no strong net internal current, the plasma is far more stable, avoiding the destructive and unpredictable disruptions of the plasma that Tokamaks see.
Essentially, stellarators owe their capabilities to computer aided design (CAD) which allow the magnetic configuration of their three dimensional coils to be designed. Additionally, 3D printing simplified the manufacture of these complex 3d coils. Finally, rather than using magnetic fields to heat the plasma as in tokamaks, stellarators use devices known as gyrotrons to create electron cyclotron resonance heating in the plasma. When combined with neutral beam injection and ion cyclotron resonance heating, the plasma can be heated throughout the different modes of operation.
Venture capital-backed interest in commercial stellarators took off in the late 2010s with a number of companies launching themselves. In many cases they spun out of university research efforts into stellarator operations, such as those from Max Planck Institute for Plasma Physics and the University of Wisconsin. The most advanced of these is the Wendelstein (W7-X) stellarator, located at the Max Planck Institute for Plasma Physics in Germany. In 2025, W7-X achieved a new world record for the “triple product” (a key metric of plasma density, temperature, and energy confinement time) for 43 seconds, surpassing previous long-pulse tokamak results.
A number of private companies are now looking to create commercial stellarators. These include Renaissance Fusion, Proxima Fusion, Type One Energy, and Thea Energy. In particular, Type 1 Energy and the Tennessee Valley Authority (TVA) are planning to build a 350 MWe (electrical output) production power plant in Clinton, TN. Similarly, Proxima Fusion, in conjunction with RWE, the Free State of Bavaria, and the Max Planck Institute for Plasma Physics are building what they deem as the world’s first commercial fusion power plant in Germany. Both are expected to be completed in the 2030s.
Conclusion: The First Part of Magnetic Fusion Energy Exploration
Magnetic fusion energy predates inertial fusion energy for no other reason because magnets have been around far longer than lasers have. It has exactly been the advances in magnets, especially HTS magnets, that have made magnetic fusion devices achieve what they could do today, which has been to come close to achieving triple product in functional devices. In the next article in this series, we’ll look at some of the more non-traditional forms of magnetic fusion energy, such as Z-pinch machines, field-reversed configurations (FRCs), and magnetic mirrors.
