What is a tokamak?

How it works

At the center of a tokamak is a ring-shaped vacuum chamber. Air and impurities are pumped out. Hydrogen gas is fed in. A strong electrical current strips electrons from its atoms to form plasma. Because plasma particles are charged, magnetic coils around the vessel can shape the plasma and keep it away from the walls, the ITER Organization explains. ITER puts the temperature needed for fusion at 150 million degrees Celsius.

The U.S. Department of Energy (DOE) describes three sets of magnets. One set of coils produces a field circling the ring the long way. A central solenoid adds one looping the short way. Together they form a twisted field that confines the plasma. A third set controls the plasma's shape and position.

Where the name comes from

The word is a Russian acronym for toroidal chamber with magnetic coils, ITER says. DOE says the first tokamak, T-1, began operating in Russia in 1958. ITER dates the design's development by Soviet researchers to the late 1960s. DOE says fusion scientists regard tokamaks as the leading confinement concept for future power plants.

Where things stand in 2026

The record for fusion power in a magnetic confinement device is 16 megawatts, according to ITER. It says the Joint European Torus (JET) produced that in 1997 from 24 megawatts of heating power, a ratio of 0.67. EUROfusion announced in February 2024 that JET, in the UK, had set a fusion energy record of 69.26 megajoules in a single six-second pulse. JET stopped operating at the end of 2023.

ITER, the international tokamak being built in southern France, is designed to produce 500 megawatts of fusion power from 50 megawatts of heating power. The ITER Organization said on July 29, 2026 that six of the nine sector modules forming the machine's core were in place, with the last expected by mid-2027. Its timeline, under a baseline approach its council approved in 2024, lists research operations starting in 2034 and deuterium-tritium operation in 2039.

Commonwealth Fusion Systems, a private developer, is building a tokamak called SPARC in Devens, Massachusetts. The company says SPARC will pass net energy, a threshold it labels Q>1, in 2027. TechCrunch reported in July 2026 that the company expected scientific breakeven in 2027. It also said only one fusion device, at the National Ignition Facility, had reached that mark. The date is a company projection.