Editing Electron gun

{{Short description|Electrical component producing a narrow electron beam}}
{{Refimprove|date=March 2020}}
[[file:Egun.jpg|thumb|Electron gun from a [[cathode-ray tube]]]]
[[file:Vidicon Electron Gun.jpg|thumb|The electron gun from an [[RCA]] [[Vidicon]] [[video camera tube]]]]

An '''electron gun''' (also called '''electron emitter''') is an electrical component in some [[vacuum tube]]s that produces a narrow, [[collimation|collimated]] [[electron beam]] that has a precise [[kinetic energy]].

The largest use is in [[cathode-ray tube]]s (CRTs), used in older [[television set]]s, [[computer display]]s and [[oscilloscope]]s, before the advent of [[flat-panel displays]]. Electron guns are also used in [[field-emission display|field-emission displays (FEDs)]], which are essentially flat-panel displays made out of rows of extremely small cathode-ray tubes. They are also used in microwave linear beam [[vacuum tube]]s such as [[klystron]]s, [[inductive output tube]]s, [[travelling-wave tube]]s, and [[gyrotron]]s, as well as in scientific instruments such as [[electron microscope]]s and [[particle accelerators]].

Electron guns may be classified by the type of electric field generation (DC or RF), by emission mechanism ([[thermionic emission|thermionic]],  [[photocathode]], [[field electron emission|cold emission]], [[Plasma (physics)|plasmas]] source), by focusing (pure electrostatic or with magnetic fields), or by the number of electrodes.

== Design ==
[[file:Kathodestraalbuis2.jpg|thumb|left|Electron gun from an [[oscilloscope]] CRT]]
[[file:Electron Gun with Wehnelt Cylinder.svg|thumb|Setup of an electron gun. 1. [[Hot cathode]]. 2. [[Wehnelt cylinder]]. 3. Anode]]

A direct current, electrostatic thermionic electron gun is formed from several parts: a [[hot cathode]], which is heated to create a stream of [[electrons]] via [[thermionic emission]]; electrodes generating an [[electric field]] to focus the electron beam (such as a [[Wehnelt cylinder]]); and one or more [[anode]] electrodes which accelerate and further focus the beam. A large voltage difference between the cathode and anode accelerates the electrons away from the cathode. A repulsive ring placed between the electrodes focuses the electrons onto a small spot on the anode, at the expense of a lower extraction field strength on the cathode surface. There is often a hole through the anode at this small spot, through which the electrons pass to form a collimated beam before reaching a second anode, called the collector. This arrangement is similar to an [[Einzel lens]].

An RF electron gun<ref name="Kirk">H.G. Kirk, R. Miller, D. Yeremian, ''Electron guns and pre-injectors'', pp. 99-103, in A. W. Chao and M. Tigner, Editors, "Accelerator Physics and Engineering" World Scientific, Singapore, 1998 </ref> consists of a [[Microwave cavity]], either single cell or multi-cell, and a [[cathode]]. In order to obtain a smaller [[beam emittance]] at a given beam current, a [[photocathode]] is used.<ref>I. Ben-Zvi,  ''photoinjectors'', pp. 158-175, in A. W. Chao, H.O. Moser and Z. Zhao, Editors, "Accelerator Physics and Technology Applications" World Scientific, Singapore, 2004 </ref> An RF electron gun with a photocathode is called a [[photoinjector]]. 

[[File:Photoinjector operating at 2856 MHz.jpg|thumb|right|A photoinjector based on a "one and a half cells" microwave cavity at a frequency of 2856 MHz.]]

Photoinjectors play a leading role in X-ray [[Free-electron laser]]s and small [[beam emittance]] [[accelerator physics]] facilities.

== Applications ==
[[file:Schottky-Emitter 01.jpg|thumb|left|Schottky-emitter electron source of an [[electron microscope]]]]

The most common use of electron guns is in [[cathode-ray tube]]s, which were widely used in computer and television monitors before the advent of flat screen displays. Most color cathode-ray tubes incorporate three electron guns, each one producing a different stream of electrons. Each stream travels through a [[shadow mask]] where the electrons will impinge upon either a [[RGB colour model|red, green or blue]] [[phosphor]] to light up a color [[pixel]] on the screen. The resultant color that is seen by the viewer will be a combination of these three [[primary color]]s.

An [[electron]] gun can also be used to [[ionize]] particles by adding electrons to, or removing electrons from an [[atom]]. This technology is sometimes used in [[mass spectrometry]] in a process called [[electron ionization]] to ionize [[vaporized]] or [[gaseous]] particles. More powerful electron guns are used for welding, metal coating, [[Electron-beam additive manufacturing|3D metal printer]]s, metal powder production and vacuum furnaces.

Electron guns are also used in medical applications to produce [[X-rays]] using a linac (linear accelerator); a high energy electron beam hits a target, stimulating emission of [[X-rays]].

Electron guns are also used in [[travelling-wave tube]] amplifiers for microwave frequencies.<ref name=THTW2015>{{Cite journal|first1=Jack|last1=Copeland|first2=Andre A.|last2=Haeff|title=The True History of the Traveling Wave Tube|journal=IEEE Spectrum| date=September 2015 |volume=52|issue=9|pages=38–43|doi=10.1109/MSPEC.2015.7226611|s2cid=36963575}}</ref>

== Measurement and detection ==
[[file:Ekanoner.jpg|thumb|Electron gun from a [[travelling-wave tube]], cutaway through axis to show construction]]

A [[nanocoulombmeter]] in combination with a [[Faraday cup]] can be used to detect and measure the beams emitted from electron gun and [[ion gun]]s.

Another way to detect electron beams from an electron gun is by using a [[phosphor]] screen which will glow when struck by an electron.

== See also ==
* [[Optics]]
* [[Electron-beam technology]]

== References ==
{{refs}}

== External links ==
* [https://virtuelle-experimente.de/en/kanone/klassisch/simulation.php Simulation of an Electron Gun] Interactive tutorial from LMU Munich
* [https://www.classe.cornell.edu/~hoff/LECTURES/08S_688/08S_688_080225.pdf ''Introduction to Electron Guns for Accelerators'' Dunham 2008]
{{Electron microscopy}}

[[Category:Electron beam]]
[[Category:Accelerator physics]]
[[Category:Microscope components]]
[[Category:Vacuum tubes]]