Cockcroft–Walton generator

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The Cockcroft–Walton (CW) generator, or multiplier, is an electric circuit that generates a high DC voltage from a low voltage AC or pulsing DC input. It was named after the British and Irish physicists John Douglas Cockcroft and Ernest Thomas Sinton Walton, who in 1932 used this circuit design to power their particle accelerator, performing the first artificial nuclear disintegration in history.[1] They used this voltage multiplier cascade for most of their research, which in 1951 won them the Nobel Prize in Physics for "Transmutation of atomic nuclei by artificially accelerated atomic particles". Less well known is the fact that the circuit was discovered much earlier, in 1919, by Heinrich Greinacher, a Swiss physicist. For this reason, this doubler cascade is sometimes also referred to as the Greinacher multiplier. Cockcroft-Walton circuits are still used in particle accelerators, but now also in many everyday electronic devices that require high voltages, such as x-ray machines, television sets, and photocopiers.


A simple two-stage CW multiplier
Output with some capacitor on a CW circuit
A full-wave CW multiplier


Operation of the CW multiplier, or any voltage doubler, is quite simple. Considering the simple two-stage version diagramed within, which is attached to an AC power source on the left side of the diagram. At the time when the AC input reaches its negative pole the leftmost diode is allowing current to flow from the ground into the first capacitor, filling it up. When the same AC signal reverses polarity, current flows through the second diode filling up the second capacitor with both the positive end from AC source and the first capacitor, charging the second capacitor to twice the charge held in the first. With each change in polarity of the input, the capacitors add to the upstream charge and boost the voltage level of the capacitors downstream, towards the output on the right. The output voltage, assuming perfect conditions, is twice the peak input voltage multiplied by the number of stages in the multiplier.

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CW multipliers are typically used to develop higher voltages for relatively low current applications, such as bias voltages ranging from tens or hundreds of volts to millions of volts for high-energy physics experiments or lightning safety testing. CW multipliers are also found, with a higher number of stages, in laser systems, high-voltage power supplies, X-ray systems, LCD backlighting, traveling wave tube amplifiers, ion pumps, electrostatic systems, air ionisers, particle accelerators, copy machines, scientific instrumentation, oscilloscopes, television sets and CRTs, bug zappers and many other applications that use high-voltage DC.

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