Science Made Simple: What Is a Tokamak?

ITER fusion reactor tokamak.
Credit: ITER   ANIMATION

A tokamak is a machine that confines a plasma using magnetic fields in a donut shape that scientists call a torus. Fusion energy scientists believe that tokamaks are the leading plasma confinement concept for future fusion power plants.

In a tokamak, magnetic field coils confine plasma particles to allow the plasma to achieve the conditions necessary for fusion. One set of magnetic coils generates an intense “toroidal” field, directed the long way around the torus. A central solenoid (a magnet that carries electric current) creates a second magnetic field directed along the “poloidal” direction, the short way around the torus.

The two field components result in a twisted magnetic field that confines the particles in the plasma. A third set of field coils generates an outer poloidal field that shapes and positions the plasma.

Basic tokamak components include the toroidal field coils (in blue), the central solenoid (in green), and poloidal field coils (in grey). The total magnetic field (in black) around the torus confines the path of travel of the charged plasma particles. Credit: Image courtesy of EUROfusion

The first tokamak, T-1, began operation in Russia in 1958. Subsequent advances led to the construction of the Tokamak Fusion Test Reactor at Princeton Plasma Physics Laboratory and Joint European Torus in England, both of which achieved record fusion power in the 1990s. These successes motivated 35 nations to collaborate on the superconducting ITER tokamak, which aims to explore the physics of burning plasmas.

Quick Tokamak Facts

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