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A Marx generator is an electrical circuit making use of multiple storage devices called capacitors. These are charged in parallel and then discharged in sequence, producing a high-voltage electrical pulse. The device is commonly used in the testing of high-voltage components and aircraft instrumentation to simulate the type of power surge that might result from a lightning strike. The generator was developed by German engineer Erwin Marx in 1924.
Technically, a Marx generator is a voltage multiplier. This type of circuit converts lower voltage alternating current (AC) to a higher direct current (DC) voltage. Usually, this is done using capacitors and diodes. Capacitors are used to store an electric charge. Diodes inhibit discharge by permitting an electric current to pass in only one direction.
The charging and discharge of the capacitors in a Marx generator is controlled by a series of resistors and spark gaps. Resistors introduce electrical resistance into a circuit, making it difficult for current to flow in that direction. Spark gaps consist of two conductors separated by a gap across which a an electric spark passes. This happens when the voltage difference between the conductors reaches a critical point called the breakdown voltage.
Resistors connect the power supply to the capacitors while limiting their discharge rate. When triggered, the spark gaps connect the capacitors in a series allowing their stored energy to discharge as a single output. For this to happen, the spark gaps must all fire more quickly than any one capacitor can discharge through its resistor. This is seldom a problem, as spark gaps typically reach the required breakdown voltage level in a matter of nanoseconds.
These devices are a common way of generating high voltage electrical impulses for testing, particularly if the voltage of the available charging supply is insufficient. When used in the testing of high-voltage equipment, a Marx generator is capable of producing electrical discharges in excess of two million volts. The Z machine, a powerful X-ray generator at the Sandia National Laboratories in New Mexico, employs a ring of 36 Marx generators. They have also been used to supply short electrical pulses for electro-optic equipment, to drive certain types of lasers and in the ignition of explosives.
A similar ladder-type circuit is used in the Cockcroft-Walton generator. In this implementation of the circuit, diodes rather than resistors and spark gaps are used for switching. The device also acts as a voltage multiplier but produces a constant DC rather that the pulsed power of a Marx generator.
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