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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Electrostatic generator | 4/5 | https://en.wikipedia.org/wiki/Electrostatic_generator | reference | science, encyclopedia | 2026-05-05T09:36:55.653201+00:00 | kb-cron |
The Van de Graaff generator was invented by American physicist Robert J. Van de Graaff in 1929 at MIT as a particle accelerator. The first model was demonstrated in October 1929. In the Van de Graaff machine, an insulating belt transports electric charge to the interior of an insulated hollow metal high voltage terminal, where it is transferred to the terminal by a "comb" of metal points. The advantage of the design was that since there was no electric field in the interior of the terminal, the charge on the belt could continue to be discharged onto the terminal regardless of how high the voltage on the terminal was. Thus the only limit to the voltage on the machine is ionization of the air next to the terminal. This occurs when the electric field at the terminal exceeds the dielectric strength of air, about 30 kV per centimeter. Since the highest electric field is produced at sharp points and edges, the terminal is made in the form of a smooth hollow sphere; the larger the diameter the higher the voltage attained. The first machine used a silk ribbon bought at a five and dime store as the charge transport belt. In 1931 a version able to produce 1,000,000 volts was described in a patent disclosure. The Van de Graaff generator was a successful particle accelerator, producing the highest energies until the late 1930s when the cyclotron superseded it. The voltage on open air Van de Graaff machines is limited to a few million volts by air breakdown. Higher voltages, up to about 25 megavolts, were achieved by enclosing the generator inside a tank of pressurized insulating gas. This type of Van de Graaff particle accelerator is still used in medicine and research. Other variations were also invented for physics research, such as the Pelletron, that uses a chain with alternating insulating and conducting links for charge transport. Small Van de Graaff generators are commonly used in science museums and science education to demonstrate the principles of static electricity. A popular demonstration is to have a person touch the high voltage terminal while standing on an insulated support; the high voltage charges the person's hair, causing the strands to stand out from the head.
=== Others ===
Not all electrostatic generators use the triboelectric effect or electrostatic induction. Electric charges can be generated by electric currents directly. Examples are ionizers and ESD guns.
== Applications ==
=== Gridded ion thruster ===
=== EWICON === An electrostatic vaneless ion wind generator, the EWICON, has been developed by The School of Electrical Engineering, Mathematics and Computer Science at Delft University of Technology (TU Delft). Its stands near Mecanoo, an architecture firm. The main developers were Johan Smit and Dhiradj Djairam. Other than the wind, it has no moving parts. It is powered by the wind carrying away charged particles from its collector. The design suffers from poor efficiency.
=== Dutch Windwheel === The technology developed for EWICON has been reused in the Dutch Windwheel.
=== Air ioniser ===
== Fringe science and devices == These generators have been used, sometimes inappropriately and with some controversy, to support various fringe science investigations. In 1911, George Samuel Piggott received a patent for a compact double machine enclosed within a pressurized box for his experiments concerning radiotelegraphy and "antigravity". Much later (in the 1960s), a machine known as "Testatika" was built by German engineer, Paul Suisse Bauman, and promoted by a Swiss community, the Methernithans. Testatika is an electromagnetic generator based on the 1898 Pidgeon electrostatic machine, said to produce "free energy" available directly from the environment.
== See also == Electrostatic motor Electrometer (also known as the "electroscope") Electret Static electricity
== References ==