Small Van de Graaff machines are produced for entertainment, and for physics education to teach electrostatics; larger ones are displayed in some science museums.

[2] The voltage produced by an open-air Van de Graaff machine is limited by arcing and corona discharge to about 5 MV.

[1][5] A more immediate inspiration for Van de Graaff was a generator W. F. G. Swann was developing in the 1920s in which charge was transported to an electrode by falling metal balls, thus returning to the principle of the Kelvin water dropper.

[12] In 1933, Van de Graaff built a 40 ft (12 m) model at MIT's Round Hill facility, the use of which was donated by Colonel Edward H. R.

[13] One consequence of the location of this generator in an aircraft hangar was the "pigeon effect": arcing from accumulated droppings on the outer surface of the spheres.

[19][page needed] By the 1970s, as much as 14 MV could be achieved at the terminal of a tandem that used a tank of high-pressure sulfur hexafluoride (SF6) gas to prevent sparking by trapping electrons.

This allowed the generation of heavy ion beams of several tens of MeV, sufficient to study light-ion direct nuclear reactions.

The greatest potential sustained by a Van de Graaff accelerator is 25.5 MV, achieved by the tandem in the Holifield Radioactive Ion Beam Facility in Oak Ridge National Laboratory.

It consisted of a tandem Van de Graaff generator operating routinely at 20 MV, housed in a distinctive building 70 m high.

Higher potentials on the sphere can also be achieved by using a voltage source to charge the belt directly, rather than relying solely on the triboelectric effect.

A Van de Graaff generator terminal does not need to be sphere-shaped to work, and in fact, the optimum shape is a sphere with an inward curve around the hole where the belt enters.

A rounded terminal minimizes the electric field around it, allowing greater potentials to be achieved without ionization of the air, or other dielectric gas, surrounding it.

The maximal achievable potential is roughly equal to the sphere radius R multiplied by the electric field Emax at which corona discharges begin to form within the surrounding gas.

[25] The initial motivation for the development of the Van de Graaff generator was as a source of high voltage to accelerate particles for nuclear physics experiments.

[25] Particle-beam Van de Graaff accelerators are often used in a "tandem" configuration with the high potential terminal located at the center of the machine.

This configuration results in two accelerations for the cost of one Van de Graaff generator and has the added advantage of leaving the ion source instrumentation accessible near ground potential.

[25] The pelletron is a style of tandem accelerator designed to overcome some of the disadvantages of using a belt to transfer charge to the high voltage terminal.

This chain of spheres serves the same function as the belt in a traditional Van de Graff accelerator – to convey charge to the high voltage terminal.

For these generators, however, corona discharge from exposed metal parts at high potentials and poorer insulation result in smaller voltages.

In the Van de Graaff generator, the belt allows the transport of charge into the interior of a large hollow spherical electrode.

This is the ideal shape to minimize leakage and corona discharge, so the Van de Graaff generator can produce the greatest voltage.