The 184-inch synchrocyclotron was first operated in November 1946. With a maximum dee voltage of only 20,000 volts, it accelerated deuterons to 190 Mev and alpha particles to 380 Mev.[4] In 1949 it was modified to permit production of 350-Mev protons also. Between 1955 and 1957 the synchrocyclotron was rebuilt so that now the following energies can be obtained: Protons Deuterons Alpha Particles Helium-3 nuclei[5] ------- --------- --------------- --------------- 730 Mev 460 Mev 910 Mev 1140 Mev In reaching an energy of 730 Mev a proton, for example, makes 75,000 revolutions in just 6 milliseconds (msec). It travels a distance of 450 miles and attains a velocity of 152,000 miles per second, or 82% of the speed of light! During this brief journey its mass increases 75%, giving very convincing evidence for the validity of Einstein's theory. Similar data for other ions may be found in the appendix. FOOTNOTES: [4] A deuteron is the nucleus of an atom of heavy hydrogen and contains one proton and one neutron; it carries a single positive electric charge. An alpha particle is the nucleus of a helium atom and is made up of two protons and two neutrons; it carries two positive charges. [5] The machine is equipped for helium-3 operation, but to date it has not been used for that purpose. DESIGN AND CONSTRUCTION OF THE 184-INCH SYNCHROCYCLOTRON _Magnet_ During the rebuilding of the cyclotron, the diameter of the magnet pole pieces was increased from 184 to 188-3/4 inches. Also, the pole gap at the center was reduced from 21 to 14 inches. These changes increased the weight of steel in the magnet from 3700 to 4000 tons. The main exciting coils, which contain 1300 turns of copper-bar conductor each, were not altered. Two auxiliary coils containing 425 turns each were added. This brought the total weight of copper from 300 to 340 tons. The coils are layer-wound around the pole pieces close to the pole gap. Other data about the coils are given in the appendix. The effect of these modifications was to increase the field strength at the center of the pole gap from 15,000 to 23,400 gauss. This increase made it possible to obtain the higher-energy ions. Power is supplied to the coils by two motor generator sets, which produce the direct current required for a steady magnetic field. The direct current from the motor generators is regulated so that the magnetic-field fluctuation is less than one part in 10,000. This is necessary if one wants an external beam of nearly uniform energy.