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How does a tokamak confine high-temperature plasma?

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laser-activated fusion — nuclear fusion Interior of the U.S. Department of Energy's National Ignition Facility (NIF), located at Lawrence Livermore National Laboratory, Livermore, California. The NIF target chamber uses a high-energy laser to heat fusion fuel to temperatures sufficient for thermonuclear ignition. The facility is used for basic science, fusion energy research, and nuclear weapons testing.

A tokamak confines high-temperature plasma within a doughnut-shaped (toroidal) vacuum chamber using a complex system of magnetic fields. To maintain stable equilibrium and prevent particles from drifting into the chamber walls, the device utilizes a helical magnetic field composed of two distinct parts:12

Toroidal field: Produced by external coils surrounding the vacuum chamber, this component points the long way around the torus.2
Poloidal field: Directed the short way around the machine, this component is generated by a strong electric current flowing within the plasma itself.2

The combination of these fields forces magnetic lines of force into a spiral or helical path. While the toroidal field provides the primary confinement, the poloidal field is essential for stability; without it, the plasma would develop distortions and strike the walls. This current can be driven via Faraday’s law of induction, radio-frequency waves, or neutral-beam injection. Additionally, a spontaneous "bootstrap current" often arises due to pressure differentials within the plasma, further aiding confinement.23