The cyclotron was invented in 1932 by Ernest O. Lawrence and M. S. Livingston at Berkeley. Particles or ions are injected into the center of two hollow D-shaped objects called "dees". A magnetic field is applied to them that is perpendicular to the plane in which they move and they accelerate across a gap between the dees by a potential difference. The orbit radius increases and eventually the particles gain energy and are ejected to hit a target. It is one of the earliest types of accelerators in use today.