English: The vacuum chamber of a cyclotron particle accelerator from 1935 with its cover off, showing the two accelerating electrodes or "dees". This was the 27 inch cyclotron built by Ernest O. Lawrence at Univ. of California Berkeley Radiation Laboratory in 1932 that could accelerate deuterons to 4 Mev. In operation, this vacuum chamber was sandwiched between the 27 in. diameter pole pieces of a huge 75 ton electromagnet which produced a vertical magnetic field of 16,000 gauss with a current of 65 A in its windings. The two hollow sheet copper "D" shaped electrodes, or "dees" 22 in. diameter by 2 in. high, form a cylindrical space within which the particles, hydrogen or duterium ions, travel. The vertical magnetic field bends the particle's path into a circle. An oscillating radio frequency potential of 13,000 volts from an electronic oscillator at about 12 MHz is applied between the two dees through the two feedlines at right rear. Each time the particles cross the gap the electric field accelerates them. The particles travel in a spiral path clockwise from the center of the dees to the rim, where they pass out of the dees through a gap and strike a target located at bottom right.