What’s a Marx generator?

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A Marx generator is an electrical circuit that uses capacitors charged in parallel and discharged in sequence to produce high voltage pulses. It is used for testing high voltage components and aircraft instrumentation. The charging and discharging is controlled by resistors and spark gaps. It can generate electrical discharges in excess of two million volts and has been used for electro-optical equipment, lasers, and explosives. A similar ladder circuit is used in the Cockcroft-Walton generator.

A Marx generator is an electrical circuit that uses 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 testing high voltage components and aircraft instrumentation to simulate the type of surge that could result from a lightning strike. The generator was developed by the German engineer Erwin Marx in 1924.

Technically, a Marx generator is a voltage multiplier. This type of circuit converts lower voltage alternating current (AC) into higher voltage direct current (DC). Usually, this is done using capacitors and diodes. Capacitors are used to store an electric charge. Diodes inhibit the discharge by allowing an electric current to flow in only one direction.

The charging and discharging of the capacitors in a Marx generator is controlled by a series of resistors and a spark gap. 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 through which an electric spark passes. This happens when the voltage difference between the conductors reaches a critical point called the breakdown voltage.

Resistors connect power to capacitors by limiting their rate of discharge. When triggered, spark gaps connect capacitors in series allowing their stored energy to discharge as a single output. For this to happen, the spark gaps must all turn on faster than a capacitor can discharge across its resistor. This is rarely a problem, as spark gaps typically reach the required breakdown voltage level in a matter of nanoseconds.

These devices are a common way to generate high voltage electrical pulses for testing, particularly if there is insufficient charging supply voltage available. When used in testing 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 Sandia National Laboratories in New Mexico, employs a ring of 36 Marx generators. They have also been used to deliver short electrical pulses for electro-optical equipment, to drive some types of lasers, and to ignite explosives.

A similar ladder circuit is used in the Cockcroft-Walton generator. In this circuit implementation, diodes are used for switching instead of resistors and spark gap. The device also acts as a voltage multiplier but produces a constant direct current rather than the pulsed power of a Marx generator.




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