Wiktionary
voltage multiplier
n. An electronic circuit that provides an output voltage higher than the input voltage, by means of capacitors and diodes
Wikipedia
Voltage multiplier
thumb|right|280px|Villard cascade voltage multiplier.
A voltage multiplier is an electrical circuit that converts AC electrical power from a lower voltage to a higher DC voltage, typically using a network of capacitors and diodes.
Voltage multipliers can be used to generate a few volts for electronic appliances, to millions of volts for purposes such as high-energy physics experiments and lightning safety testing. The most common type of voltage multiplier is the half-wave series multiplier, also called the Villard cascade (but actually invented by Heinrich Greinacher).