A toroidal magnetic confinement device that combines externally generated magnetic fields with a large internally driven plasma current to confine fusion fuel — the most experimentally advanced path to controlled fusion energy.
The tokamak was invented in the Soviet Union in the late 1950s by physicists Igor Tamm and Andrei Sakharov. The name is a Russian acronym: toroidal'naya kamera s magnitnymi katushkami (“toroidal chamber with magnetic coils”). Early Soviet experiments, particularly the T-3 tokamak, demonstrated electron temperatures of ~1 keV in 1968 — a verified achievement confirmed by a visiting British team using Thomson scattering.[1]
The plasma current is usually driven inductively by a central solenoid. Steady-state operation requires non-inductive current drive methods.[2]
Safety factor (q): Stability requires q > 1 throughout most of the plasma, with q ≥ 2–3 at the edge.[2]
Plasma beta (β): Typical tokamak betas range from 1% to 5%, though spherical tokamaks have achieved above 40% transiently.[3]
Aspect ratio (A = R/a): Conventional tokamaks have A ≈ 3; compact spherical tokamaks operate at A ≈ 1.5.[2]
JET set a verified record of 69 MJ of fusion energy in a single D–T pulse and was retired in 2024. ITER will be the world’s largest tokamak (major radius 6.2 m, plasma current 15 MA), targeting Q ≥ 10. First plasma is expected in the early 2030s.[3]
The path requires solving: tritium breeding, neutron-resistant materials, disruption avoidance, and sustained high-duty-cycle operation. Several national and private efforts are designing demonstration power plants (DEMO).[4]