How it began
Fusion research in the Soviet Union began in 1950. In October of that year Igor Tamm and his former postgraduate student Andrei Sakharov proposed confining high-temperature plasma in a toroidal device with a longitudinal magnetic field. Experiments began in 1951 at what is now the Kurchatov Institute in Moscow, led by Lev Artsimovich. The first devices had vessels of glass, porcelain or metal with insulating inserts. T-1, which began operating in 1958, is considered the first tokamak.
Before it existed
In the early years of magnetic confinement research, several kinds of device evolved side by side, including pinches, stellarators and magnetic traps. The z-pinch and the stellarator also tried to produce helical field lines but showed serious instabilities. Soviet researchers first explored the tokamak principle in small table-top toroids with ceramic vessels; because that material contaminated the plasma, T-1 was built with a steel chamber.
How it works
A tokamak uses a powerful magnetic field generated by external magnets to confine plasma in the shape of a torus, or ring. A central solenoid and toroidal and poloidal magnets shape the plasma, and a stable equilibrium requires magnetic field lines that wind around the torus in a helix. The name comes from the Russian for toroidal chamber and magnetic coils and was probably suggested by Igor Golovin, a deputy director of the laboratory that became the Kurchatov Institute.
How it spread
In 1958 the Soviet Union, the United States and the United Kingdom began sharing fusion research. The T-3 tokamak reached an electron temperature of about 10 million degrees, and in 1968 British scientists from Culham confirmed the result with a laser scattering measurement. Princeton's Model C stellarator was rebuilt as a tokamak in 1969 and confirmed the findings. By the mid-1970s dozens of tokamaks were in use around the world.
What lasted
The T-3 collaboration was the first international collaboration in nuclear fusion and established the tokamak as a promising option for magnetic confinement. In the late 1970s the Kurchatov Institute tested the first superconducting magnets and divertors in tokamaks, features now found in large designs.
Where it stands today
The tokamak is the leading candidate among magnetic confinement designs for producing controlled fusion power. The ITER tokamak, under construction in France, is the main global fusion research effort and is aimed for completion by 2034. Because a tokamak requires a continuously changing magnetic field, modern machines sustain their plasma discharges on timescales of seconds or minutes.
