Last updated
High-power 140 GHz gyrotron for plasma heating in the Wendelstein 7-X fusion experiment, Germany. W7-X gyrotron.jpg
High-power 140 GHz gyrotron for plasma heating in the Wendelstein 7-X fusion experiment, Germany.

A gyrotron is a class of high-power linear-beam vacuum tubes which generates millimeter-wave electromagnetic waves by the cyclotron resonance of electrons in a strong magnetic field. Output frequencies range from about 20 to 527 GHz, [1] [2] covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from tens of kilowatts to 1–2 megawatts. Gyrotrons can be designed for pulsed or continuous operation. The gyrotron was invented by soviet scientists [3] at NIRFI, based in Nizhny Novgorod, Russia.


Principle of operation

Diagram of a gyrotron Gyrotron.png
Diagram of a gyrotron

The gyrotron is a type of free-electron maser which generates high-frequency electromagnetic radiation by stimulated cyclotron resonance of electrons moving through a strong magnetic field. [4] [5] It can produce high power at millimeter wavelengths because as a fast-wave device its dimensions can be much larger than the wavelength of the radiation. This is unlike conventional microwave vacuum tubes such as klystrons and magnetrons, in which the wavelength is determined by a single-mode resonant cavity, a slow-wave structure, and thus as operating frequencies increase, the resonant cavity structures must decrease in size, which limits their power-handling capability.

In the gyrotron a hot filament in an electron gun at one end of the tube emits an annular-shaped (hollow tubular) beam of electrons, which is accelerated by a high-voltage anode and then travels through a large tubular resonant cavity structure in a strong axial magnetic field, usually created by a superconducting magnet around the tube. The field causes the electrons to move helically in tight circles around the magnetic field lines as they travel lengthwise through the tube. At the position in the tube where the magnetic field reaches its maximum the electrons radiate electromagnetic waves in a transverse direction (perpendicular to the axis of the tube) at their cyclotron resonance frequency. The millimeter radiation forms standing waves in the tube, which acts as an open-ended resonant cavity, and is formed into a beam, which radiates through a window in the side of the tube into a waveguide. The spent electron beam is absorbed by a collector electrode at the end of the tube.

As in other linear-beam microwave tubes, the energy of the output electromagnetic waves comes from the kinetic energy of the electron beam, which is due to the accelerating anode voltage. In the region before the resonant cavity where the magnetic field strength is increasing, it compresses the electron beam, converting the longitudinal drift velocity to transverse orbital velocity, in a process similar to that occurring in a magnetic mirror used in plasma confinement. [5] The orbital velocity of the electrons is 1.5 to 2 times their axial beam velocity. Due to the standing waves in the resonant cavity, the electrons become "bunched"; that is, their phase becomes coherent (synchronized) so they are all at the same point in their orbit at the same time. Therefore, they emit coherent radiation.

The electron speed in a gyrotron is slightly relativistic (on the order of but not close to the speed of light). This contrasts to the free-electron laser (and xaser) that work on different principles and whose electrons are highly relativistic.


Gyrotrons are used for many industrial and high-technology heating applications. For example, gyrotrons are used in nuclear fusion research experiments to heat plasmas and also in manufacturing industry as a rapid heating tool in processing glass, composites, and ceramics, as well as for annealing (solar and semiconductors). Military applications include the Active Denial System.


The output window of the tube from which the microwave beam emerges can be in two locations. In the transverse-output gyrotron, the beam exits through a window in the side of the tube. This requires a 45° mirror at the end of the cavity to reflect the microwave beam, positioned at one side so the electron beam misses it. In the axial-output gyrotron, the beam exits through a window in the end of the tube at the far end of the cylindrical collector electrode which collects the electrons.

The original gyrotron developed in 1964 was an oscillator, but since that time gyrotron amplifiers have been developed. The helical gyrotron electron beam can amplify an applied microwave signal similarly to the way a straight electron beam amplifies in classical microwave tubes such as the klystron, so there are a series of gyrotrons which function analogously to these tubes. Their advantage is that they can operate at much higher frequencies. The gyro-monotron (gyro-oscillator) is a single-cavity gyrotron that functions as an oscillator. A gyro-klystron is an amplifier that functions analogously to a klystron tube. Has two microwave cavities along the electron beam, an input cavity upstream to which the signal to be amplified is applied and an output cavity downstream from which the output is taken. A gyro-TWT is an amplifier that functions analogously to a travelling wave tube (TWT). It has a slow wave structure similar to a TWT paralleling the beam, with the input microwave signal applied to the upstream end and the amplified output signal taken from the downstream end. A gyro-BWO is an oscillator that functions analogously to a backward wave oscillator (BWO). It generates oscillations traveling in an opposite direction to the electron beam, which are output at the upstream end of the tube. A gyro-twystron is an amplifier that functions analogouly to a twystron, a tube that combines a klystron and a TWT. Like a klystron it has an input cavity at the upstream end followed by buncher cavities to bunch the electrons, which are followed by a TWT type slow-wave structure which develops the amplified output signal. Like a TWT it has a wide bandwidth.


The gyrotron was invented in the Soviet Union. [6] Present makers include Communications & Power Industries (USA), Gycom (Russia), Thales Group (EU), Toshiba (Japan), and Bridge12 Technologies. System developers include Gyrotron Technology.

See also

Related Research Articles

Electronic oscillator electronic circuit that produces a repetitive, oscillating electronic signal, often a sine wave or a square wave

An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices ranging from simplest clock generators to digital instruments and complex computers and peripherals etc. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.

Maser Microwave Amplification by Stimulated Emission of Radiation

A maser is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, James P. Gordon, and Herbert J. Zeiger at Columbia University in 1953. Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are used as the timekeeping device in atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes and deep space spacecraft communication ground stations.

Microwave Form of electromagnetic radiation

Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter; with frequencies between 300 MHz (1 m) and 300 GHz (1 mm). Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF bands. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.

Cavity magnetron device for generating microwaves

The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities. Electrons pass by the openings to these cavities and cause microwaves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening. The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions. Unlike other vacuum tubes such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier in order to increase the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube.

Resonance phenomenon in which a vibrating system or external force drives another system to oscillate with greater amplitude at specific frequencies

In physics, resonance describes the phenomena of amplification that occurs when the frequency of a periodically applied force is in harmonic proportion to a natural frequency of the system on which it acts. When an oscillating force is applied at a resonant frequency of a dynamical system, the system will oscillate at a higher amplitude than when the same force is applied at other, non-resonant frequencies.


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.

Traveling-wave tube device used to amplify radio frequency signals in the microwave spectrum

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. 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:

Resonator Device or system that exhibits resonance

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 resonator can be either electromagnetic or mechanical. Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones. Another example is quartz crystals used in electronic devices such as radio transmitters and quartz watches to produce oscillations of very precise frequency.

An optical parametric amplifier, abbreviated OPA, is a laser light source that emits light of variable wavelengths by an optical parametric amplification process. It is essentially the same as an optical parametric oscillator, but without the optical cavity.

Gunn diode diode

A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1962 by physicist J. B. Gunn. Its largest use is in electronic oscillators to generate microwaves, in applications such as radar speed guns, microwave relay data link transmitters, and automatic door openers.

Crossed-field amplifier

A crossed-field amplifier (CFA) is a specialized vacuum tube, first introduced in the mid-1950s and frequently used as a microwave amplifier in very-high-power transmitters.

Backward-wave oscillator

A backward wave oscillator (BWO), also called carcinotron or backward wave tube, is a vacuum tube that is used to generate microwaves up to the terahertz range. Belonging to the traveling-wave tube family, it is an oscillator with a wide electronic tuning range.

Here, is a list of initialisms and acronyms used in laser physics, applications and technology.

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 gains of 20–23 dB at frequencies up to about a gigahertz.

Particle accelerator device to propel charged particles to high speeds

A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

Microwave cavity

A microwave cavity or radio frequency (RF) cavity is a special type of resonator, consisting of a closed metal structure that confines electromagnetic fields in the microwave region of the spectrum. The structure is either hollow or filled with dielectric material. The microwaves bounce back and forth between the walls of the cavity. At the cavity's resonant frequencies they reinforce to form standing waves in the cavity. Therefore, the cavity functions similarly to an organ pipe or sound box in a musical instrument, oscillating preferentially at a series of frequencies, its resonant frequencies. Thus it can act as a bandpass filter, allowing microwaves of a particular frequency to pass while blocking microwaves at nearby frequencies.

Terahertz metamaterial

A terahertz metamaterial is a class of composite metamaterials designed to interact at terahertz (THz) frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz.

Barkhausen–Kurz tube high frequency vacuum tube electronic oscillator

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.

Sutton tube

A Sutton tube, or reflex klystron, is a type of vacuum tube used to generate microwaves. It is a low-power device used primarily for two purposes; one is to provide a tuneable low-power frequency source for the local oscillators in receiver circuits, and the other, with minor modifications, as a switch that could turn on and off another microwave source. The second use, sometimes known as a soft Sutton tube or rhumbatron switch, was a key component in the development of microwave radar by Britain during World War II. Microwave switches of all designs, including these, are more generally known as T/R tubes or T/R cells.

Extended interaction oscillator

The extended interaction oscillator (EIO) is a linear-beam vacuum tube designed to convert direct current to RF power. The conversion mechanism is the space charge wave process whereby velocity modulation in an electron beam transforms to current or density modulation with distance.


  1. Richards, Mark A.; William A. Holm (2010). "Power Sources and Amplifiers". Principles of Modern Radar: Basic Principles. SciTech Pub., 2010. p. 360. ISBN   978-1891121524.
  2. Blank, M.; Borchard, P.; Cauffman, S.; Felch, K.; Rosay, M.; Tometich, L. (2013-06-01). Experimental demonstration of a 527 GHz gyrotron for dynamic nuclear polarization. 2013 Abstracts IEEE International Conference on Plasma Science (ICOPS). p. 1. doi:10.1109/PLASMA.2013.6635226. ISBN   978-1-4673-5171-3.
  3. High-Magnetic-Field Research and Facilies (1979). Washington, D.C.: National Academy of Sciences. p. 51.
  4. "What is a Gyrotron?". Learn about DNP-NMR spectroscopy. Bridge 12 Technologies. Retrieved July 9, 2014.
  5. 1 2 Borie, E. (c. 1990). "Review of Gyrotron Theory" (PDF). EPJ Web of Conferences. KfK 4898. 149: 04018. Bibcode:2017EPJWC.14904018N. doi:10.1051/epjconf/201714904018 . Retrieved July 9, 2014.
  6. National Research Council (U.S.). Panel on High Magnetic Field Research and Facilities (1979). "Defense Technology - High Frequency Radiation". High-Magnetic-Field Research and Facilities. Washington, D.C.: National Academy of Sciences. pp. 50–51. OCLC   13876197.