Van de Graaff generator

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on an insulated, hollow metal terminal, creating electric potential. Because it moves charge mechanically, it supplies high voltage direct current at very low current. American physicist Robert J. Van de Graaff invented the generator in 1929 and first demonstrated it in 1931. He conceived of the generator as a power source for particle accelerators, as high potentials can be used to accelerate subatomic particles to high energies in an evacuated accelerator tube. Beginning with Van de Graaff’s Round Hill machine in 1933, Van de Graaff accelerators were widely used in nuclear science research through the 1970s. Several high-energy Van de Graaff accelerators remain in scientific use and have inspired related electrostatic accelerator designs. Lower-energy Van de Graaff generators have been used to generate energetic particle beams for nuclear science, nuclear medicine, and ion implantation. In open air, Van de Graaff generators can reach a potential difference of as much as 5 megavolts (MV); generators enclosed in pressurized tanks reach potentials of 25 MV. An inexpensive tabletop version can produce on the order of 100 kV, enough energy to discharge visible electric sparks. Because they are simple to build and produce only microamperes of current, small Van de Graaff generators are used for science demonstrations and personal entertainment; larger demonstration models are displayed in some science museums.