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. Its application is mainly in the area of electronic warfare, by way of interfering with electronic equipment such as radars or radio equipment.
Vircator schematic
A typical vircator is built inside an evacuatedresonant 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 transmission line. The pulse has a 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.[1] 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.[2]
Function
The massive short pulse of high voltage causes the cathode to emit an intense burst of electrons by the field electron emission 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.
U.S. patent 4,345,220, High power microwave generator using relativistic electron beam in waveguide drift tube, to Donald J. Sullivan, 1982
U.S. 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"
Related Research Articles
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A vacuum tube, electron tube, valve, or tube is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
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A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range. Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, while high-power klystrons are used as output tubes in UHF television transmitters, satellite communication, radar transmitters, and to generate the drive power for modern particle accelerators.
This is an index of articles relating to electronics and electricity or natural electricity and things that run on electricity and things that use or conduct electricity.
A traveling-wave tube or traveling-wave tube amplifier is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. It was invented by Andrei Haeff around 1933 as a graduate student at Caltech, and its present form was invented by Rudolf Kompfner in 1942–43. The TWT belongs to a category of "linear beam" tubes, such as the klystron, in which the radio wave is amplified by absorbing power from a beam of electrons as it passes down the tube. Although there are various types of TWT, two major categories are:
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A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal semiconductor electronic component, with negative differential resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1962 by physicist J. B. Gunn. Its main uses are in electronic oscillators to generate microwaves, in applications such as radar speed guns, microwave relay data link transmitters, and automatic door openers.
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The Fleming valve, also called the Fleming oscillation valve, was a thermionic valve or vacuum tube invented in 1904 by English physicist John Ambrose Fleming as a detector for early radio receivers used in electromagnetic wireless telegraphy. It was the first practical vacuum tube and the first thermionic diode, a vacuum tube whose purpose is to conduct current in one direction and block current flowing in the opposite direction. The thermionic diode was later widely used as a rectifier — a device that converts alternating current (AC) into direct current (DC) — in the power supplies of a wide range of electronic devices, until beginning to be replaced by the selenium rectifier in the early 1930s and almost completely replaced by the semiconductor diode in the 1960s. The Fleming valve was the forerunner of all vacuum tubes, which dominated electronics for 50 years. The IEEE has described it as "one of the most important developments in the history of electronics", and it is on the List of IEEE Milestones for electrical engineering.
The inductive output tube (IOT) or klystrode is a variety of linear-beam vacuum tube, similar to a klystron, used as a power amplifier for high frequency radio waves. It evolved in the 1980s to meet increasing efficiency requirements for high-power RF amplifiers in radio transmitters. The primary commercial use of IOTs is in UHF television transmitters, where they have mostly replaced klystrons because of their higher efficiencies and smaller size. IOTs are also used in particle accelerators. They are capable of producing power output up to about 30 kW continuous and 7 MW pulsed and power gains of 20–23 dB at frequencies up to about a gigahertz.
The Barkhausen–Kurz tube, also called the retarding-field tube, reflex triode, B–K oscillator, and Barkhausen oscillator was a high frequency vacuum tube electronic oscillator invented in 1920 by German physicists Heinrich Georg Barkhausen and Karl Kurz. It was the first oscillator that could produce radio power in the ultra-high frequency (UHF) portion of the radio spectrum, above 300 MHz. It was also the first oscillator to exploit electron transit time effects. It was used as a source of high frequency radio waves in research laboratories, and in a few UHF radio transmitters through World War 2. Its output power was low which limited its applications. However it inspired research that led to other more successful transit time tubes such as the klystron, which made the low power Barkhausen-Kurz tube obsolete.
A noise generator is a circuit that produces electrical noise. Noise generators are used to test signals for measuring noise figure, frequency response, and other parameters. Noise generators are also used for generating random numbers.
In electronics, a micropup is a style of triode vacuum tube (valve) developed by the British General Electric Company (GEC) during World War II for use at very high frequencies such as those used in radar. The first micropup, the VT90, was introduced in 1939 and capable of operating at wavelengths as low as 25 cm, although at low power. The VT90 was much more widely used in a broad variety of radars operating in the 1.5 m band, around 200 MHz, which remained in widespread use for the rest of the war. Improved versions like the NT99 of 1941 allowed operations at 50 cm, or 600 MHz, leading to a series of new radar sets. These saw less use as the introduction of production-quality cavity magnetrons the same year led to microwave-frequency radars that outperformed the best micropups.
James Nelson Benford is an American physicist, High-Power Microwave (HPM) scientist, book author, science-fiction writer, and entrepreneur, best known for introducing novel technological concepts and conjectures related to the exploration of outer space, among these the design of laser-driven sailships, the possible use of co-orbital objects by alien probes to spy on earth, and the appraisal of technical and safety issues associated with the Search for Extraterrestrial Intelligence (SETI). He was born in Mobile, Alabama in 1941, as was his twin brother, science-fiction author Greg Benford. He has two children, the eldest being Dominic Benford, an astrophysicist and the Program Scientist for the Nancy Grace Roman Space Telescope.
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