Van de Graaff Generator, an electric induction machine used in nuclear research and cancer therapy. The Van de Graaff generator is a particle accelerator, a device for increasing the velocity, and therefore the energy, of atoms and subatomic particles. It consists of a hollow metal sphere mounted on a hollow column that insulates the sphere from the ground.
A moving cloth belt inside the column carries electrons from a battery up to the sphere, where they are deposited. As the electrons accumulate, the sphere obtains an increasingly higher electric charge. Finally, the difference in electric potential between the sphere and the ground is so great that the charge rushes down through the column back to the ground. The electrons have a high velocity, and can be channeled into other apparatus to bombard various materials to release other subatomic particles or to produce X rays.
The generator was invented in 1928 by Robert Jemison Van de Graaff of the Massachusetts Institute of Technology.