RBS Instrumentation: Voltage Sources

The oldest form of accelerator is the Van de Graaff, named for Robert Van de Graaff, who put a suggestion by Lord Kelvin into practice. Its distinguishing feature is charge transfer on a moving belt with one pulley at ground and the other at the terminal. Charge is placed on the belt by a comb of corona points. A second set of points removes the charge at the terminal. Although the traditional Van de Graaff accelerator is single-ended, the voltage source can be used in a tandem machine.

A well-known variation is the Pelletron which is identical to a Van de Graaff, except that a chain with alternate links (pellets) of metal and insulator replaces the belt. This chain provides more uniform charge transport than the belt, resulting in more stable voltage.

A Tandetron accelerator uses a voltage doubler power supply fed by a radio frequency signal. There are no moving parts, reducing the need for expensive maintenance. The voltage from the Tandetron device is also very stable. Terminal voltage stability influences spectroscopic resolution.

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