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How does magnetic confinement hold a hot plasma in place?

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3D illustration of the interior reaction chamber of a tokamak fusion reactor, showing a large, cylindrical, metallic structure with curved walls and bright light panels. — fusion reactor A tokamak is a device used in nuclear-fusion research for magnetic confinement of plasma.

Magnetic confinement holds hot plasma in place by utilizing magnetic fields to control the motion of charged particles. Because plasma consists of electrons and ions, these particles experience a Lorentz force when moving through a magnetic field, causing them to spiral around lines of force rather than striking the reactor walls.12

To maintain a stable equilibrium, the magnetic force must balance the expansive pressure exerted by the plasma's thermal energy. Confinement configurations generally fall into two categories:1

Toroidal (Closed) Configurations: Devices like the tokamak use a doughnut-shaped torus to eliminate end losses. By creating a helical magnetic field—combining toroidal and poloidal components—the system ensures particles remain trapped in stable orbits.132
Linear (Open) Configurations: These use magnetic mirroring to reflect particles back toward the center by increasing the magnetic field strength at the ends of the device. To further reduce leakage, electrostatic plugging is often employed to create a barrier for the nuclei.42