Cutaway drawing of the Westinghouse Atom Smasher, a Van de Graaff generator built in 1937 at the Westinghouse Corporation research center at Forest Hills, Pennsylvania, USA. It consists of a Van de Graaff generator which generates 5 million volts (MV) on its dome shaped electrode, which is used to accelerate charged subatomic particles through an evacuated tube parallel to the generator's charge carrying belt. Since open-air Van de Graaff machines are limited to about 1 MV by leakage of current from its electrode by arcs and corona discharge, the machine is enclosed in an onion-shaped air tank pressurized to a pressure of 120 pounds per square inch, which allows it to reach a voltage of 5 MV.