Van de Graaff Generator

Van de Graaff GeneratorVan de Graaff generator is a high-voltage generator operating under the principle of electrification of a moving dielectric tape. Robert Van de Graaf, an American physic, was the first who created such generator in 1929.The generator consists of a rubber or silk dielectric tape on rollers. The upper roller is dielectric, and the other is a metal one. This metal roller is connected to the earth. One of dielectric tape's ends is in a metal sphere. Electrode brushes are installed at a small distance at the top and at the bottom each. The upper electrode is connected to the sphere's inner surface while electric potential of some kilo volts is applied to the lower one. Positive ions occur at the lower roller as a result of air ionization. Coulomb force makes them move toward the earthed roller and settle on the tape . Therefore, upward moving tape is charged. The tape delivers the charge into the sphere where it is tapped off by brushes. All charges are displaced to the sphere's surface; its inner surface's potential always equals to 0 while its external surface accumulates the electric charge.Such generator generates substantial potential differences of dozens of kilo volts. However, they are rarely used in practice. Van de Graaff generators are used to modulate electro static processes, for instance, to imitate lightning dischargers and accelerate particles.

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Science & Technology

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• generator
• history of technics
• operating principle