What is "vircator"

n. virtual cathode oscillator

A vircator (VIRtual CAthode oscillaTOR) is a microwave generator that is capable of generating brief pulses of tunable, narrow band microwaves at very high power levels.

A typical vircator is built inside an evacuated resonant cavity or waveguide. An electrode, a cold cathode, at one end injects an intense electron beam, such as from a Marx generator or a flux compression generator, optionally with a suitable pulse forming network, e.g. a Blumlein. The pulse has magnitude in the range of hundred or more kilovolts and duration of about 50-150 nanoseconds. The electrons are attracted to a thin anode, such as an aluminized PET film or a stainless steel mesh, that is connected to the grounded waveguide body. The unit is surrounded by a magnet. Due to the intensity of the electron beam, many electrons pass through the anode into the region beyond it, forming a virtual cathode. The electron beam must be so intense as to exceed the space charge limiting current in that region, causing oscillations that generate microwaves. The frequency, efficiency and other characteristics of the emitted beam depend on the precise physical configuration and operating parameters.

A coaxial design exists where the cathode forms an outer ring surrounding the anode cylinder, with the virtual cathode forming along the cylinder's axis. Such design can be directly integrated with a waveguide.

The frequencies are usually in the region of 0.5-1.5, 2-6, 3, or 5-18 GHz. Other frequencies are also possible. Lower frequencies are usable for jamming communications, higher frequencies can be harnessed for their destructive effects on electronics.

Vircators have been used as electromagnetic pulse generators and for generating X-rays. Power levels on the order of 10 to 10 watts are possible.

A design successor of a vircator is a reditron, which has higher efficiency and narrower bandwidth.