tokamaks

A tokamak is a type of magnetic confinement fusion device that uses a combination of toroidal and poloidal magnetic fields to confine hot plasma in a torus, with the aim of sustaining thermonuclear fusion reactions. The name comes from Russian words meaning toroidal chamber with magnetic coils.

The central feature is a strong toroidal magnetic field produced by external coils, plus a poloidal field generated by a current driven through the plasma; together they create a helical magnetic field that confines charged particles and reduces cross-field transport.

A typical tokamak consists of a doughnut-shaped vacuum vessel surrounded by toroidal field coils, a central solenoid that drives the plasma current, and supplementary poloidal-field coils. Plasma heating is provided by ohmic heating, plus auxiliary methods such as neutral beam injection and radiofrequency heating. Magnetic confinement is designed to minimize energy losses long enough to approach or surpass breakeven, where fusion power exceeds the heating power.

Challenges include plasma instabilities and turbulent transport, such as sawtooth oscillations and edge-localized modes. Research focuses on improving confinement, controlling stability, and developing materials capable of withstanding neutron flux.

The tokamak design emerged in the 1950s in the Soviet Union and rapidly became the leading approach to magnetic confinement fusion. It underpins large international projects such as ITER in France and many national facilities. Tokamaks are used to study plasma behavior, heating, current drive, and materials science essential for future fusion power plants.