Britannica Sources used in this answer

Why do charged particles spiral around magnetic field lines in a fusion reactor?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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.

In a fusion reactor, charged particles spiral around magnetic field lines due to the Lorentz force. When a charged particle moves through a magnetic field, it experiences a force that is perpendicular to both its velocity and the direction of the magnetic field.12

This force acts as a centripetal force, causing the particle to gyrate or orbit around the magnetic field lines. If the particle has a velocity component parallel to the magnetic field, it continues to move along the field line while simultaneously gyrating, which results in a helical or spiral trajectory.12

This behavior is fundamental to magnetic confinement, as it allows the reactor to trap high-temperature plasma and prevent it from striking the bounding walls of the device. By guiding particles along these field lines, researchers can maintain the stable equilibrium necessary for controlled nuclear fusion.3