Video narration
How can a charged particle keep gaining energy inside a compact machine? Think of pushing a swing at the right moment. Inside a cyclotron, it moves between two D-shaped electrodes called dees. An alternating voltage creates an electric field across the gap, giving the particle a kick each time it crosses. But the magnetic field is not the accelerator. It does no work; it only changes direction, bending the particle into a semicircle and returning it to the gap. The voltage reverses at the right time. Each crossing adds energy; the magnetic field turns the particle around. As it gets faster, the semicircles grow, forming an outward spiral in the top-down path. At very high speeds, the timing eventually fails. So how does it keep speeding up? By getting an electric kick at every gap crossing, while the magnetic field bends it into the next loop.