The Cockcroft -Walton accelerator ( Cockcroft -Walton also sometimes called generator, although this really only the high voltage is described producing part of the plant ) is a loop with a DC type of particle accelerators.
His developers John Cockcroft and Ernest Walton thus succeeded in 1930 provided the first evidence of a triggered by artificially accelerated particles nuclear reaction - then proudly referred to as nuclear disintegration. Lithium was irradiated with protons of kinetic energy 300 keV. The reaction products of helium -4 nuclei ( alpha particles ) were observed. It involved the reaction
The actual acceleration of the part is a Van de Graaff accelerator, very similar: a straight tube, is maintained in the high vacuum and oriented in the longitudinal direction, a stationary electric field. The difference is that the acceleration voltage is generated by a high-voltage cascade. The potential of the accelerating tube rings need not, as in the Van de Graaff accelerator a resistor chain as a voltage divider, but can easily be connected to the individual voltage levels of the cascade.
Through difficulties to the isolation of very high voltages ( leakage, corona discharge), the achievable voltage as in Van de Graaff facilities is limited to a few mega volts.
For operation of the ion source, a power supply within the high-voltage electrode (terminal) is required. They may consist of a generator which is driven by an insulating shaft of a motor located at ground potential. For small plants, for example, 200 kilovolt also be treated by a highly insulating transformer is possible.
The high voltage must not, as in Van de Graaff electrostatic systems engineering ( mechanical transport of charge on a moving insulator ) can be built, but is recovered via transformer and voltage multiplier from the power grid. Therefore Cockcroft -Walton systems are also suitable for applications with relatively high current intensity of the particle beam ( up to many milliamps ). On the other hand, their high voltage and thus the particle energy is less accurate constant but has ripple through getting some blur on.
Cockroft -Walton accelerator play as an independent accelerator facilities for basic research in physics hardly an issue. However, they are used in many large accelerators such as synchrotrons as the first acceleration stage right at the exit of the ion source.