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How does Earth’s magnetic field trap charged particles in the Van Allen radiation belts?

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Diagram showing a circular loop of wire with an electric current, surrounded by curved blue lines representing magnetic field lines that loop around the wire and pass through its center. — magnetism Some lines of the magnetic field B (blue) for an electric current I (gold) in a loop.

Earth’s magnetic field traps charged particles within the Van Allen radiation belts through the interaction of Lorentz forces and the planet's dipole geometry.12

The process involves three primary types of particle motion:

Gyration: Charged particles move in spiral paths around magnetic field lines due to the Lorentz force.13
Magnetic Mirroring: As particles travel along field lines toward the poles, they encounter converging magnetic field lines. This convergence creates a "mirror force" that reflects the particles, causing them to bounce back and forth between the Northern and Southern hemispheres.132
Azimuthal Drift: Due to the curvature of field lines and the decrease in magnetic field strength with distance from Earth, particles slowly drift longitudinally around the planet. Protons typically drift westward, while electrons drift eastward.12

Together, these motions confine energetic particles—originating from cosmic rays, the solar wind, or the atmosphere—within two concentric, doughnut-shaped zones. Over time, collisions with atmospheric atoms can remove these particles from the belts.132