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{{Short description|Vacuum tube used for amplifying radio waves}}
{{for-multi|the high-speed switching arc-discharge tube|Krytron|the klystrode|Inductive output tube}}
{{More citations needed|date=January 2013}}
[[File:Klystron.jpg|250px|thumb|right|400&nbsp;kW klystron used for spacecraft communication at the [[Canberra Deep Space Communications Complex]]. This is a spare in storage.]]
[[File:Klystron tube 1952.jpg|thumb|upright=2|5&nbsp;kW klystron tube used as power amplifier in UHF television transmitter, 1952. When installed, the tube projects through holes in the center of the cavity resonators, with the sides of the cavities making contact with the metal rings on the tube.]]

A '''klystron''' is a specialized linear-beam [[vacuum tube]], invented in 1937 by American electrical engineers [[Russell and Sigurd Varian]],<ref name=tubeguys>Pond, Norman H. "The Tube Guys". Russ Cochran, 2008 p.31-40</ref> which is used as an [[amplifier]] for high [[radio frequencies]], from [[ultra high frequency|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 transmitter]]s, [[satellite communication]], [[radar]] [[transmitter]]s, and to generate the drive power for modern [[particle accelerator]]s.

In a klystron, an [[electron beam]] interacts with radio waves as it passes through [[cavity resonator|resonant cavities]], metal boxes along the length of a tube.<ref name="Gilmour">{{cite book | last = Gilmour | first = A. S. | title = Klystrons, Traveling Wave Tubes, Magnetrons, Cross-Field Amplifiers, and Gyrotrons | publisher = Artech House | date = 2011 | pages = 3–4 | url = https://books.google.com/books?id=l_1egQKKWe4C&q=magnetron+%22negative+resistance&pg=PA490 | isbn = 978-1608071845}}</ref> The electron beam first passes through a cavity to which the input signal is applied. The energy of the electron beam amplifies the signal, and the amplified signal is taken from a cavity at the other end of the tube. The output signal can be coupled back into the input cavity to make an [[electronic oscillator]] to generate radio waves. The [[Gain (electronics)|power gain]] of klystrons can be high, up to 60&nbsp;dB (an increase in signal power of a factor of one million), with output power up to tens of [[megawatt]]s, but the [[Bandwidth (signal processing)|bandwidth]] is narrow, usually a few percent although it can be up to 10% in some devices.<ref name="Gilmour" />

A ''reflex klystron'' is an obsolete type in which the [[electron beam]] was reflected back along its path by a high potential electrode, used as an oscillator.

==Etymology==
The name ''klystron'' comes from the [[Ancient Greek|Greek]] verb κλύζω (''klyzo'') referring to the action of waves breaking against a shore, and the suffix -τρον ("tron") meaning the place where the action happens.<ref name="ReferenceA">{{cite journal |last1=Varian |first1=R. H. |last2=Varian |first2=S. F. |year=1939 |title=A High Frequency Oscillator and Amplifier |journal=[[Journal of Applied Physics]] |volume=10 |issue=5 |pages=321 |bibcode = 1939JAP....10..321V |doi=10.1063/1.1707311}}</ref> The name "klystron" was suggested by [[Hermann Fränkel]], a professor in the classics department at Stanford University when the klystron was under development.<ref>Varian, Dorothy. "The Inventor and the Pilot". Pacific Books, 1983 p. 189</ref>

==History==
[[File:Prototype klystron cutaway.jpg|thumb|upright=1.8|The first commercial klystron, manufactured by Westinghouse in 1940. Part of the tube is cut away to show the internal construction. On the left are the cathode and accelerating anode, which create the electron beam. In the center between the wooden supports is the drift tube, surrounded by the two donut-shaped cavity resonators: the "buncher" and the "catcher". The output terminal is visible at top. On the right is the cone shaped collector anode, which absorbs the electrons. It could generate 200&nbsp;W of power at a wavelength of 40&nbsp;centimeters (750&nbsp;MHz) with 50% efficiency.]]

The klystron was the first significantly powerful source of radio waves in the [[microwave]] range; before its invention the only sources were the [[Barkhausen–Kurz tube]] and [[split-anode magnetron]], which were limited to very low power. It was invented by the brothers [[Russell and Sigurd Varian]] at [[Stanford University]]. Their prototype was completed and demonstrated successfully on August 30, 1937.<ref>Varian, Dorothy. ''The Inventor and the Pilot''. Pacific Books, 1983 p. 187</ref> Upon publication in 1939,<ref name="ReferenceA"/> news of the klystron immediately influenced the work of US and UK researchers working on [[radar]] equipment. The Varians went on to found [[Varian Associates]] to commercialize the technology (for example, to make small [[linear accelerators]] to generate photons for external beam [[radiation therapy]]). Their work was preceded by the description of velocity modulation by A. Arsenjewa-Heil and [[Oskar Heil]] (wife and husband) in 1935, though the Varians were probably unaware of the Heils' work.<ref name="Heil">{{cite journal|author=George Caryotakis|date=November 18, 1997|title=Invited paper: The Klystron: A microwave source of surprising range and endurance|url=http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-7731.pdf|url-status=dead|journal=American Physics Society: Division of Plasma Physics Conference, Pittsburgh, PA|publisher=Stanford, CA: Stanford SLAC|archive-url=https://web.archive.org/web/20150924102609/http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-7731.pdf|archive-date=September 24, 2015|access-date=September 18, 2012}}</ref>

The work of physicist [[W. W. Hansen]] was instrumental in the development of the klystron and was cited by the Varian brothers in their 1939 paper. His resonator analysis, which dealt with the problem of accelerating electrons toward a target, could be used just as well to decelerate electrons (i.e., transfer their kinetic energy to RF energy in a resonator). During the Second World War, Hansen lectured at the MIT Radiation labs two days a week, commuting to Boston from [[Sperry Gyroscope Company]] on Long Island. His resonator was called a "rhumbatron" by the Varian brothers.<ref name=tubeguys /> Hansen died of [[beryllium disease]] in 1949 as a result of exposure to [[beryllium oxide]] (BeO).

During the Second World War, the [[Axis powers]] relied mostly on (then low-powered and long wavelength) klystron technology for their radar system microwave generation, while the Allies used the far more powerful but frequency-drifting technology of the [[cavity magnetron]] for much shorter-wavelength centimetric microwave generation. Klystron tube technologies for very high-power applications, such as [[synchrotron]]s and radar systems, have since been developed.

Right after the war, [[American Telephone and Telegraph|AT&T]] used 4-watt klystrons in its [[TD-2|brand new network]] of [[microwave relay]] links that covered the contiguous United States .<ref>Gerald W. Brock, ''The Second Information Revolution'', Harvard University Press, 2009, {{ISBN|0674028791}}, pp. 122,123</ref> The network provided long-distance telephone service and also carried television signals for the major TV networks. [[Western Union|Western Union Telegraph Company]] also built point-to-point microwave communication links using intermediate repeater stations at about 40 mile intervals at that time, using 2K25 reflex klystrons in both the transmitters and receivers. In some applications Klystrons have been replaced by solid state transistors.<ref>{{Cite web|url=https://www.lsu.edu/camd/news/2023/12/ssrfnewsarticle.php|title=CAMD Upgrades to Solid State RF|website=www.lsu.edu}}</ref> High efficiency Klystrons have been developed which have 10% more effiency than conventional Klystrons.<ref>{{Cite web|url=https://cerncourier.com/a/cern-and-canon-demonstrate-efficient-klystron/|title=CERN and Canon demonstrate efficient klystron|date=September 5, 2022|website=CERN Courier}}</ref>

== Operation ==
Klystrons amplify [[Radio frequency|RF signals]] by converting the [[kinetic energy]] in a [[Direct current|DC]] [[Cathode ray|electron beam]] into radio frequency power. In a vacuum, a beam of electrons is emitted by an [[electron gun]] or [[Hot cathode|thermionic cathode]] and accelerated by high-voltage electrodes (typically in the tens of kilovolts).

This beam passes through an input [[cavity resonator]]. RF energy has been fed into the input cavity at, or near, its [[resonant frequency]], creating [[standing wave]]s, which produce an oscillating voltage, which acts on the electron beam. The electric field causes the electrons to "bunch": electrons that pass through when the electric field opposes their motion are slowed, while electrons which pass through when the electric field is in the same direction are accelerated, causing the previously continuous electron beam to form bunches at the input frequency.

To reinforce the bunching, a klystron may contain additional "buncher" cavities.

The beam then passes through a "drift" tube, in which the faster electrons catch up to the slower ones, creating the "bunches", then through a "catcher" cavity.

In the output "catcher" cavity, each bunch enters the cavity at the time in the cycle when the electric field opposes the electrons' motion, decelerating them. Thus the kinetic energy of the electrons is converted to potential energy of the field, increasing the amplitude of the [[oscillation]]s. The oscillations excited in the catcher cavity are coupled out through a [[coaxial cable]] or [[waveguide]].

The spent electron beam, with reduced energy, is captured by a collector electrode.

To make an [[electronic oscillator|oscillator]], the output cavity can be coupled to the input cavity(s) with a [[coaxial cable]] or [[waveguide]]. [[Positive feedback]] excites spontaneous oscillations at the resonant frequency of the cavities.

==Two-cavity klystron==
[[File:Klystron.enp.gif|right]]

The simplest klystron tube is the two-cavity klystron. In this tube there are two microwave cavity resonators, the "buncher" and the "catcher". When used as an amplifier, the weak microwave signal to be amplified is applied to the buncher cavity through a coaxial cable or waveguide, and the amplified signal is extracted from the catcher cavity.

At one end of the tube is the [[hot cathode]] which produces electrons when heated by a filament. The electrons are attracted to and pass through an [[anode]] cylinder at a high positive potential; the cathode and anode act as an [[electron gun]] to produce a high velocity stream of electrons. An external [[electromagnet]] winding creates a longitudinal [[magnetic field]] along the beam axis which prevents the beam from spreading.

The beam first passes through the "buncher" cavity resonator, through grids attached to each side. The buncher grids have an oscillating AC potential across them, produced by standing wave oscillations within the cavity, excited by the input signal at the cavity's [[resonant frequency]] applied by a coaxial cable or waveguide. The direction of the field between the grids changes twice per cycle of the input signal. Electrons entering when the entrance grid is negative and the exit grid is positive encounter an electric field in the same direction as their motion, and are accelerated by the field. Electrons entering a half-cycle later, when the polarity is opposite, encounter an electric field which opposes their motion, and are decelerated.

Beyond the buncher grids is a space called the ''drift space''. This space is long enough so that the accelerated electrons catch up with electrons that were decelerated at an earlier time, forming "bunches" longitudinally along the beam axis. Its length is chosen to allow maximum bunching at the resonant frequency, and may be several feet long.

[[File:Klystron oscillator 1944.jpg|thumb|Klystron oscillator from 1944. The electron gun is on the right, the collector on the left. The two [[cavity resonator]]s are in center, linked by a short coaxial cable to provide positive feedback.]]

The electrons then pass through a second cavity, called the "catcher", through a similar pair of grids on each side of the cavity. The function of the ''catcher grids'' is to absorb energy from the electron beam. The bunches of electrons passing through excite standing waves in the cavity, which has the same resonant frequency as the buncher cavity. Each bunch of electrons passes between the grids at a point in the cycle when the exit grid is negative with respect to the entrance grid, so the electric field in the cavity between the grids opposes the electrons motion. The electrons thus do work on the electric field, and are decelerated, their [[kinetic energy]] is converted to electric [[potential energy]], increasing the amplitude of the oscillating electric field in the cavity. Thus the oscillating field in the catcher cavity is an amplified copy of the signal applied to the buncher cavity. The amplified signal is extracted from the catcher cavity through a coaxial cable or waveguide.

After passing through the catcher and giving up its energy, the lower energy electron beam is absorbed by a "collector" electrode, a second anode which is kept at a small positive voltage.

===Klystron oscillator===
An [[electronic oscillator]] can be made from a klystron tube, by providing a [[feedback]] path from output to input by connecting the "catcher" and "buncher" cavities with a [[coaxial cable]] or [[waveguide (electromagnetism)|waveguide]]. When the device is turned on, [[electronic noise]] in the cavity is amplified by the tube and fed back from the output catcher to the buncher cavity to be amplified again. Because of the high [[Q factor|Q]] of the cavities, the signal quickly becomes a sine wave at the [[resonant frequency]] of the cavities.

==Multicavity klystron==
In all modern klystrons, the number of cavities exceeds two. Additional "buncher" cavities added between the first "buncher" and the "catcher" may be used to increase the gain of the klystron or to increase the bandwidth.<ref>{{citation|title=Microwave Devices and Circuits|publisher=Dorling Kinderley|isbn=978-81-7758-353-3|page=380|date=September 1990}}</ref>

The residual kinetic energy in the electron beam when it hits the collector electrode represents wasted energy, which is dissipated as heat, which must be removed by a cooling system. Some modern klystrons include depressed collectors, which recover energy from the beam before collecting the electrons, increasing efficiency. Multistage depressed collectors enhance the energy recovery by "sorting" the electrons in energy bins.

==Reflex klystron==
[[File:ExKlystron.jpg|thumb|upright=1.5|Low-power Soviet reflex klystron from 1963. The [[cavity resonator]] from which the output is taken is attached to the electrodes labeled ''Externer Resonator''. Reflex klystrons are almost obsolete now.]]
[[File:Reflex klystron schematic-en.svg|right]]
[[File:Varian V-260 model.jpg|thumb|left|alt=cutaway of a mechanically tuned reflex klystron|cutaway: mechanically tuned reflex klystron<ref>{{Cite web|url=https://www.radiomuseum.org/tubes/tube_v-260.html|title=V- 260, Tube V-260; Röhre V- 260 ID35571, Reflex Klystron|website=www.radiomuseum.org|access-date=2019-12-03}}</ref>
]]
{{main|Sutton tube}}

The [[reflex klystron]] (also known as a [[Sutton tube]] after one of its inventors, Robert Sutton) was a low power klystron tube with a single cavity, which functioned as an [[electronic oscillator|oscillator]]. It was used as a [[local oscillator]] in some radar receivers and a [[modulator]] in microwave transmitters in the 1950s and 1960s, but is now obsolete, replaced by semiconductor microwave devices.

In the reflex klystron the electron beam passes through a single resonant cavity. The electrons are fired into one end of the tube by an [[electron gun]]. After passing through the resonant cavity they are reflected by a negatively charged reflector electrode for another pass through the cavity, where they are then collected. The electron beam is velocity modulated when it first passes through the cavity. The formation of electron bunches takes place in the drift space between the reflector and the cavity. The [[volt]]age on the reflector must be adjusted so that the bunching is at a maximum as the electron beam re-enters the resonant cavity, thus ensuring a maximum of energy is transferred from the electron beam to the [[Radio frequency|RF]] oscillations in the cavity. The reflector voltage may be varied slightly from the optimum value, which results in some loss of output power, but also in a variation in frequency. This effect is used to good advantage for automatic frequency control in receivers, and in [[frequency modulation]] for transmitters. The level of modulation applied for transmission is small enough that the power output essentially remains constant. At regions far from the optimum voltage, no oscillations are obtained at all.<ref>{{citation|title=Reflex klystron|publisher=Dorling Kinderley|isbn=978-81-7758-353-3|pages=391, 392|date=September 1990}}</ref>
There are often several regions of reflector voltage where the reflex klystron will oscillate; these are referred to as modes. The electronic tuning range of the reflex klystron is usually referred to as the variation in frequency between half power points&mdash;the points in the oscillating mode where the power output is half the maximum output in the mode.

Modern [[semiconductor]] technology has effectively replaced the reflex klystron in most applications.

== Gyroklystron ==

[[File:Picture of a Coaxial Gyrokylstron Tube.jpg|thumb|Picture of a three cavity coaxial gyroklystron tube, University of Maryland, IREAP]]

The gyroklystron is a microwave amplifier with operation dependent on the [[Electron cyclotron resonance|cyclotron resonance]] condition.<ref>{{Cite book |last=Nusinovich |first=Gregory S. |title=Introduction to the physics of gyrotrons |publisher=The Johns Hopkins University Press |year=2004 |isbn=0-8018-7921-3 |location=Baltimore, Maryland}}</ref>
Similarly to the klystron, its operation depends on the modulation of the electron beam, but instead of axial bunching the modulation forces alter the cyclotron frequency and hence the azimuthal component of motion, resulting in phase bunches. In the output cavity, electrons which arrive at the correct decelerating phase transfer their energy to the cavity field and the amplified signal can be coupled out.

[[File:Coaxial Gyroklystron, cross-sectional view.jpg|thumb|Engineering diagram of a four cavity coaxial gyroklystron at the University of Maryland, IREAP]]

The gyroklystron has cylindrical or coaxial cavities and operates with transverse electric field modes. Since the interaction depends on the resonance condition, larger cavity dimensions than a conventional klystron can be used. This allows the gyroklystron to deliver high power at very high frequencies which is challenging using conventional klystrons.<ref>{{Cite book |last=Gouveia |first=Emmanuel Steve |url=https://www.academia.edu/122732808 |title=Development of a Four Cavity Second-Harmonic Gyroklystron as Driver for a Linear Accelerator - Ph.D. Dissertation |work=University of Maryland Ph.D. Dissertation |date=2004-06-16 |publisher=University of Maryland, College Park, MD }}</ref>

== Tuning ==
[[File:Aust.-Synchrotron,-Klystron-for-Storage-Ring,-14.06.2007.jpg|right|200px|thumb|Large klystrons as used in the [[storage ring]] of the [[Australian Synchrotron]] to maintain the energy of the [[electron]] beam]]

Some klystrons have cavities that are tunable. By adjusting the frequency of individual cavities, the technician can change the operating frequency, gain, output power, or bandwidth of the amplifier. No two klystrons are exactly identical (even when comparing like part/model number klystrons). Each unit has manufacturer-supplied calibration values for its specific performance characteristics. Without this information the klystron would not be properly tunable, and hence not perform well, if at all.

Tuning a klystron is delicate work which, if not done properly, can cause damage to equipment or injury to the technician due to the very high voltages that could be produced. The technician must be careful not to exceed the limits of the graduations, or damage to the klystron can result. Other precautions taken when tuning a klystron include using nonferrous tools. Some klystrons employ permanent [[magnet]]s. If a technician uses [[ferrous]] tools (which are [[ferromagnetic]]) and comes too close to the intense magnetic fields that contain the electron beam, such a tool can be pulled into the unit by the intense magnetic force, smashing fingers, injuring the technician, or damaging the unit. Special lightweight nonmagnetic (or rather very weakly [[diamagnetic]]) tools made of [[beryllium]] alloy have been used for tuning U.S. Air Force klystrons.

Precautions are routinely taken when transporting klystron devices in aircraft, as the intense magnetic field can interfere with magnetic navigation equipment. Special overpacks are designed to help limit this field "in the field," and thus allow such devices to be transported safely.

==Optical klystron==
The technique of amplification used in the klystron is also being applied experimentally at optical frequencies in a type of [[laser]] called the [[free-electron laser]] (FEL); these devices are called ''optical klystrons''.<ref name="Bonifacio">{{cite journal|last1=Bonifacio|first1=R.|last2=Corsini|first2=R.|last3=Pierini|first3=P.|date=15 March 1992|title=Theory of the high gain optical klystron|url=http://wwwsrf.mi.infn.it/publications/papers/1992/files/PRA_45_4091.pdf|journal=Physical Review A|volume=45|issue=6|pages=4091–4096|bibcode=1992PhRvA..45.4091B|doi=10.1103/physreva.45.4091|pmid=9907460|access-date=June 24, 2014}}</ref> Instead of microwave cavities, these use devices called [[undulator]]s. The electron beam passes through an undulator, in which a laser light beam causes bunching of the electrons. Then the beam passes through a second undulator, in which the electron bunches cause oscillation to create a second, more powerful light beam.<ref name="Bonifacio" />

==Floating drift tube klystron==
The floating drift tube klystron has a single cylindrical chamber containing an electrically isolated central tube. Electrically, this is similar to the two cavity oscillator klystron with considerable feedback between the two cavities. Electrons exiting the source cavity are velocity modulated by the electric field as they travel through the drift tube and emerge at the destination chamber in bunches, delivering power to the oscillation in the cavity. This type of oscillator klystron has an advantage over the two-cavity klystron on which it is based, in that it needs only one tuning element to effect changes in frequency. The drift tube is electrically insulated from the cavity walls, and DC bias is applied separately. The DC bias on the drift tube may be adjusted to alter the transit time through it, thus allowing some electronic tuning of the oscillating frequency. The amount of tuning in this manner is not large and is normally used for frequency modulation when transmitting.

==Applications==
Klystrons can produce far higher microwave power outputs than [[solid state (electronics)|solid state]] microwave devices such as [[Gunn diode]]s. In modern systems, they are used from UHF (hundreds of megahertz) up to hundreds of gigahertz (as in the Extended Interaction Klystrons in the [[CloudSat]] satellite). Klystrons can be found at work in [[radar]], satellite and wideband high-power communication (very common in [[television]] [[broadcasting]] and EHF [[satellite]] terminals), medicine ([[radiation oncology]]), and [[high-energy physics]] ([[particle accelerator]]s and experimental reactors). At [[SLAC]], for example, klystrons are routinely employed which have outputs in the range of 50&nbsp;MW (pulse) and 50&nbsp;kW (time-averaged) at 2856&nbsp;MHz. The [[Arecibo Telescope|Arecibo Planetary Radar]] used two klystrons that provided a total power output of 1&nbsp;MW (continuous) at 2380&nbsp;MHz.<ref>{{cite journal|last=Campbell|first=D. B.|author2=Hudson, R. S. |author3=Margot, J. L. |title=Advances in Planetary Radar Astronomy|journal=Review of Radio Science|date=2002|volume=1999-2002|pages=869–899|bibcode=2002rrs..book..869C }}</ref>

Gyroklystrons have found limited military application in radars as [[traveling-wave tube]] signal amplifiers for [[active phased array radar]].{{efn|E.g. Soviet-Russian experimental «Ruza» APAR radiolocator.<ref>{{Cite journal |date=July 2000 |title=A megawatt power millimeter-wave phased-array radar |journal=[[IEEE Aerospace and Electronic Systems]] |volume=15 |issue=7|doi=10.1109/62.854021 |last1=Tolkachev |first1=A.A. |last2=Levitan |first2=B.A. |last3=Solovjev |first3=G.K. |last4=Veytsel |first4=V.V. |last5=Farber |first5=V.E. |pages=25–31 }}</ref>}}<ref>{{Cite book|last1=Du |first1=Chao-Hai |last2=Liu |first2=Pu-Kun |date=2014 |title=Millimeter-Wave Gyrotron Traveling-Wave Tube Amplifiers |doi=10.1007/978-3-642-54728-7 |isbn=978-3-642-54727-0 |url=https://link.springer.com/book/10.1007/978-3-642-54728-7 |language=en}}</ref>

''[[Popular Science]]''{{'}}s "Best of What's New 2007"<ref>{{cite web |url=http://www.popsci.com/popsci/flat/bown/2007/green/item_67.html |title=PopSci's Best of What's New 2007 |publisher=Popsci.com |access-date=2010-02-28 |archive-date=2009-03-16 |archive-url=https://web.archive.org/web/20090316094656/http://www.popsci.com/popsci/flat/bown/2007/green/item_67.html |url-status=dead }}</ref><ref>{{cite web |url=http://www.popsci.com/popsci/flat/bown/2007/innovator_2.html |title=PopSci's Best of What's New 2007 |publisher=Popsci.com |access-date=2010-02-28 |archive-date=2010-03-02 |archive-url=https://web.archive.org/web/20100302173650/http://www.popsci.com/popsci/flat/bown/2007/innovator_2.html |url-status=dead }}</ref> described a company, Global Resource Corporation, currently defunct, using a klystron to convert the [[hydrocarbons]] in everyday materials, automotive waste, [[coal]], [[oil shale]], and [[oil sands]] into [[natural gas]] and [[diesel fuel]].<ref>[http://www.patentstorm.us/patents/7629497.html US Patent 7629497 - Microwave-based recovery of hydrocarbons and fossil fuels] {{Webarchive|url=https://web.archive.org/web/20110507072722/http://www.patentstorm.us/patents/7629497.html |date=2011-05-07 }} Issued on December 8, 2009</ref>

==See also==
{{div col|colwidth=22em}}
*[[Crossed-field amplifier]]
*[[Electromagnetic radiation]]
*[[Free-electron laser]]
*[[Gyrotron]]
*[[Inductive output tube]]
*[[Linear accelerator]]
*[[Magnetron]]
*[[Backward-wave oscillator]]
*[[Particle accelerator]]
*[[Traveling-wave tube]]
*[[Waveguide]]
*[[Extended interaction oscillator]]
{{div col end}}

==Notes==
{{notelist}}

==References==
{{reflist}}

== External links ==
{{Commons category|Klystrons}}
* [https://www.youtube.com/watch?v=yCs8czNJC8o&index=30 The Klystron] ([[YouTube]]-video, describes in detail the electron gun and various klystron designs.)
* [http://www.tpub.com/neets/book11/45b.htm (Two cavity klystron)]
* [http://www.tpub.com/neets/book11/45c.htm (Multicavity klystron)]
* [http://www.tpub.com/neets/book11/45d.htm (Reflex klystron)]
* [http://www2.slac.stanford.edu/vvc/accelerators/klystron.html (High power for linear accelerator)] {{Webarchive|url=https://web.archive.org/web/20090404051206/http://www2.slac.stanford.edu/vvc/accelerators/klystron.html |date=2009-04-04 }}
* [https://archive.today/20121211064924/http://www.varianinc.com/cgi-bin/nav?corp/history/klystron&cid=KJLJIMJQFN History of the Klystron from Varian]
* [http://www2.slac.stanford.edu/vvc/accelerators/gallery/gallery.html Stanford Linear Accelerator Center (249) Klystron Gallery Pictures] {{Webarchive|url=https://web.archive.org/web/20090529021854/http://www2.slac.stanford.edu/vvc/accelerators/gallery/gallery.html |date=2009-05-29 }}
* [http://www.tubecollector.org/list.php?L=-K&M=Y&H=Klystrons Klystron collection in the Virtual Valve Museum] {{Webarchive|url=https://web.archive.org/web/20101006002924/http://www.tubecollector.org/list.php?L=-K&M=Y&H=Klystrons |date=2010-10-06 }}
* [https://web.archive.org/web/20080721003829/http://www.radartutorial.eu/08.transmitters/tx12.en.html Klystron Amplifier]
* [http://www.osti.gov/energycitations/servlets/purl/6183102-lNcpBQ/6183102.PDF "Microwave Gun"] klystron developed at the [[SLAC]]

{{Electronic component|state=collapsed}}

[[Category:Electron beam]]
[[Category:Microwave technology]]
[[Category:Accelerator physics]]
[[Category:Vacuum tubes]]
[[Category:American inventions]]