Van de Graff generator working construction
Generator is often made of right-voltage electrostatic sources for the production of “atom-smashing” devices that are useful in experiments in nuclear physics. One such generator was designed by Robert J. Van de Graaff and further developed with his associate John G. Trump.
A large metal sphere S is supported by an insulating material is motor driven by pulley C; at the upper end it passes over the idler pulley D. a series of needle points at F is kept at a high negative potential (10 to 50kV) by the source E, and a corona discharge sprays electrons onto the belt as it moves upward from C. another series of needle points at G transfer some of the electrons from the belt to the sphere S, giving it a continually increasing negative charge. A second set of needle points at H creates a high potential gradient which ionizes the air in the region. Positive ions are attracted to the belt and are carried downward to be neutralized by electrons sprayed onto the belt by the grounded set of needles at I.
Thus there is a steady transfer of negative electricity up the belt to the sphere and a downward flow of positive charges from the sphere to the ground. This results in giving the sphere a high negative potential with respect to the ground. Some large machines of this type have produced potentials up to 10 MV, and commercial models of various sizes are currently available for a variety of use. The limiting potential is determined by various leakages including the surrounding air and the supporting insulators.
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