A cyclotron is a type of circular particle accelerator that combines an alternating electric field with a uniform magnetic field to accelerate particles in a spiral trajectory. The particle beam is then straightened out and emitted from one end.
They were invented by American physicist Ernest Orlando Lawrence in 1932. They are particularly suited for low-mass particles like electrons and protons, but is not recommended from heavier ones like entire ions. They were the original particle accelerator and are still in use today in nuclear medicine due to their comparatively low cost and size. For scientific application, they were superseded by the synchrotron (1944) and the storage ring (1961).
:::image(sidebar)
The original design by Ernest O. Lawrence from his 1932 patent. The magnetic field curves the trajectory, whereas the electric field acts in the hollow between the two half-moon sections (numbered 1 and 2 in the diagram). These are also called "dees" due to their "D" shape. The particle beam comes out from the "High Speed Ions" arrow in the bottom left.
By Ernest O. Lawrence - U.S. Patent 1,948,384, Public Domain. Image from Wikipedia.
:::
Operation#
Particles are sourced from the center of the apparatus and directed using an electric field to the two surrounding sections. The electric field does work on the particle, accelerating it. Within these sections, they are deflected by a magnetic field, which does no work and only curves the trajectory by a half-circle in uniform circular motion. After the 180° turn, it passes through the electric field again, which is carefully designed to invert before this happens so that it will accelerate the particle in the opposite direction. The additional speed makes the new turn radius a little higher, creating the almost-spiral pattern we see. This process is repeated several times, with each turn adding some velocity to the particle. The particle beam is then emitted in a straight line towards the outer rim of the machine.