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How do cyclotrons use magnetic fields to accelerate charged particles?

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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.

In a cyclotron, magnetic fields are essential for guiding charged particles along a circular path, allowing them to pass repeatedly through accelerating regions.1

The device utilizes a large magnet to create a constant, uniform magnetic field perpendicular to the plane of the particle's orbit. When a charged particle moves through this field at a right angle, it experiences a Lorentz force that acts perpendicular to both the particle's velocity and the magnetic field, forcing it into a circular trajectory.2314

Inside the cyclotron, particles are housed within two hollow, D-shaped electrodes called dees. While the magnetic field keeps the particles in a circular path, an alternating electric field applied across the gap between the dees provides the energy for acceleration. Each time the particles cross this gap, the electric field accelerates them, causing their speed and orbital radius to increase. This results in a spiral-like path of continually increasing radius until the particles reach the desired energy and are extracted.234