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Anelectron gun (also calledelectron emitter) is an electrical component in somevacuum tubes that produces a narrow,collimatedelectron beam that has a precisekinetic energy.
The largest use is incathode-ray tubes (CRTs), used in oldertelevision sets,computer displays andoscilloscopes, before the advent offlat-panel displays. Electron guns are also used infield-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 beamvacuum tubes such asklystrons,inductive output tubes,travelling-wave tubes, andgyrotrons, as well as in scientific instruments such aselectron microscopes andparticle accelerators.
Electron guns may be classified by the type of electric field generation (DC or RF), by emission mechanism (thermionic,photocathode,cold emission,plasmas source), by focusing (pure electrostatic or with magnetic fields), or by the number of electrodes.
A direct current, electrostatic thermionic electron gun is formed from several parts: ahot cathode, which is heated to create a stream ofelectrons viathermionic emission; electrodes generating anelectric field to focus the electron beam (such as aWehnelt cylinder); and one or moreanode 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 anEinzel lens.
An RF electron gun[1] consists of aMicrowave cavity, either single cell or multi-cell, and acathode. In order to obtain a smallerbeam emittance at a given beam current, aphotocathode is used.[2] An RF electron gun with a photocathode is called aphotoinjector.
Photoinjectors play a leading role in X-rayFree-electron lasers and smallbeam emittanceaccelerator physics facilities.
The most common use of electron guns is incathode-ray tubes, 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 ashadow mask where the electrons will impinge upon either ared, green or bluephosphor to light up a colorpixel on the screen. The resultant color that is seen by the viewer will be a combination of these threeprimary colors.
Anelectron gun can also be used toionize particles by adding electrons to, or removing electrons from anatom. This technology is sometimes used inmass spectrometry in a process calledelectron ionization to ionizevaporized orgaseous particles. More powerful electron guns are used for welding, metal coating,3D metal printers, metal powder production and vacuum furnaces.
Electron guns are also used in medical applications to produceX-rays using a linac (linear accelerator); a high energy electron beam hits a target, stimulating emission ofX-rays.
Electron guns are also used intravelling-wave tube amplifiers for microwave frequencies.[3]
Ananocoulombmeter in combination with aFaraday cup can be used to detect and measure the beams emitted from electron gun andion guns.
Another way to detect electron beams from an electron gun is by using aphosphor screen which will glow when struck by an electron.
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