The tokamak, a Soviet doughnut of magnetism, still leads the race for fusion power
To fuse atoms the way the Sun does, fuel must be heated to tens of millions of degrees and held away from any wall. The tokamak does it with magnets, twisting a ring of plasma inside a doughnut-shaped chamber. Soviet physicists invented it in the 1950s, and it remains the leading fusion design.
Fusion itself was first achieved on Earth in 1934 by Mark Oliphant, Paul Harteck and Ernest Rutherford, who fired deuterium nuclei at a target in a particle accelerator. That approach can never pay off, because most particles scatter and lose energy instead of fusing. Useful power requires heating the whole fuel so its atoms collide constantly, hence the word thermonuclear; in 1944 Enrico Fermi estimated the reaction would sustain itself at around 50 million kelvin.
Andrei Sakharov and Igor Tamm conceived the tokamak, and experiments began in 1951 at Moscow's Kurchatov Institute under Lev Artsimovich. Its 1958 T-1 is often called the first true tokamak. The name, coined in 1957, abbreviates Russian words for a toroidal magnetic chamber; it began as tokamag until the ending was softened for sound. The breakthrough came in 1968, when British scientists at Culham confirmed the impressive results of the Soviet T-3. The key was magnetic field lines spiralling around the ring, which tamed instabilities that plagued rival designs. A worldwide rush followed, and dozens were running by the mid-1970s.
Central and outer magnets shape the plasma, while beams of neutral particles and radio-frequency waves heat it. Because the field must keep changing, each pulse lasts seconds or minutes. America's TFTR and Europe's JET first added tritium to the deuterium fuel, and JET set records still standing as of 2025, including 69 megajoules of energy and 16 megawatts of fusion power, though it never produced more energy than it consumed.
Those machines revealed problems only a far larger device could solve, too costly for one nation. After Ronald Reagan and Mikhail Gorbachev agreed in 1985 to cooperate, the ITER project emerged; construction began in Cadarache, France, in 2013, with completion aimed for 2034. Japan's JT-60SA is currently the largest operating tokamak, and private firms are proposing compact versions.
Source: Tokamak
