English: Diagram of a cyclotron, a particle accelerator invented by Earnest O. Lawrence in 1932 and widely used from the 1930s to the 1950s. It consists of a pair of "D" shaped sheet metal electrodes called "Dees" placed face to face inside a vacuum chamber, between the poles of an electromagnet. An oscillating radio frequency voltage of several thousand volts is applied to the dees. Atomic particles to be accelerated, such as protons are released in the center. The magnetic field causes them to travel in a spiral path from the center to the rim of the dees, being accelerated each time they pass from one electrode to the other. When the particles reach the rim they pass out of the dees through a small gap and strike a target. In this diagram the electromagnet pole pieces are not shown full size; they must be at least as big as the dees to create a uniform field.

Caption: How the cyclotron works. Size of the magnets has been kept down to show the path of the electron