A vircator (VIRtual CAthode oscillaTOR) is a

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

generator that is capable of generating brief pulses of tunable, narrow band microwaves at very high power levels. Its application is mainly in the area of electronic warfare, by way of interfering with electronic equipment such as radars or radio equipment. A typical vircator is built inside an evacuated

resonant cavity A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonato ...

waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...

. An electrode, a

cold cathode A cold cathode is a cathode that is not electrically heated by a filament.A negatively charged electrode emits electrons or is the positively charged terminal. For more, see field emission. A cathode may be considered "cold" if it emits more el ...

, at one end injects an intense

electron beam Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to ele ...

, such as from a

Marx generator A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are used in high-energy physics experiments, as well as to simulat ...

or a

flux compression generator An explosively pumped flux compression generator (EPFCG) is a device used to generate a high-power electromagnetic pulse by compressing magnetic flux using Explosive material#High explosives, high explosive. An EPFCG only ever generates a single ...

, optionally with a suitable

pulse forming network A pulse-forming network (PFN) is an electric circuit that accumulates electrical energy over a comparatively long time, and then releases the stored energy in the form of a relatively square pulse of comparatively brief duration for various puls ...

, 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 An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

, such as an aluminized PET film or a

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

mesh, that is connected to the grounded waveguide body. The unit is surrounded by a

magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

. Due to the intensity of the electron beam, many electrons pass through the anode into the region beyond it, forming a virtual

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

. 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

. 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 An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...

generators and for generating

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s. Power levels on the order of 10¹⁰ to 10¹² watts are possible. A design successor of a vircator is a reditron, which has higher efficiency and narrower bandwidth.

Function

The massive short pulse of high voltage causes the cathode to emit an intense burst of electrons by the

field electron emission Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However, field emissio ...

mechanism. The electrons are attracted to the anode. A large proportion of the electrons passes through the anode and forms a cloud behind it, forming the virtual cathode. However, the electrons are still attracted by the anode (and repulsed by each other), so they change direction and fly back towards the anode, only to pass through again and be repulsed by the cathode and attracted towards the anode. The rapidly accelerating and decelerating electrons, as they oscillate back and forth between the real and virtual cathode through the mesh anode at microwave frequencies, then produce electromagnetic radiation.

Sources

*, High power microwave generator using relativistic electron beam in waveguide drift tube, to Donald J. Sullivan, 1982 *{{US Patent, 4,730,170, "Virtual cathode microwave generator having annular anode slit," Thomas J. T. Kwan, 1988 *Donald J. Sullivan, "High Power Microwave Generation From a Virtual Cathode Oscillator (Vircator)," IEEE Trans. Nucl. Sci., vol. NS-30, No. 4, 3426-3428 (Aug. 1983

*Thomas J. T. Kwan, "High-Power Coherent Microwave Generation from Oscillating Virtual Cathodes," Phys. Fluids 27 (1), 228-232 (Jan. 1984) *Libor DRAŽAN, Roman VRÁNA, "Axial Vircator for Electronic Warfare Applications

Energy weapons Microwave technology Vacuum tubes