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Electron gun - Wikipedia, the free encyclopedia
8/22/11 3:49 PM
Electron gun
From Wikipedia, the free encyclopedia
An electron gun (also called electron emitter) is an electrical
component that produces an electron beam that has a precise kinetic
energy and is most often used in television sets and computer
displays which use cathode ray tube (CRT) technology, as well as
in other instruments, such as electron microscopes and particle
accelerators. Electron guns may be classified in several ways:
Electron gun from a cathode ray tube
by the type of electric field generation (DC or RF),
by emission mechanism (thermionic, photocathode, cold
emission, plasma source),
by focusing (pure electrostatic or with magnetic fields), or
by the number of electrodes.
Contents
1 Characteristics
2 Applications
3 See also
4 References
5 External links
Electron gun from an oscilloscope CRT
Characteristics
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 which
focus the beam (such as a Wehnelt cylinder), and one or more anode electrodes which accelerate and further
focus the electrons. A large voltage between the cathode and anode accelerates the electrons. A repulsive ring
placed between them focuses the electrons onto a small spot on the anode at the expense of a lower extraction
field strength on the cathode surface. Often at this spot is a hole so that the electrons that pass through the anode
form a collimated beam and finally reach a second anode called a collector. This arrangement is similar to an
Einzel lens.
An ion gun consists of a cylinder where gas enters from one end face, undergoes electron bombardment from
the side walls, and is subjected to an extraction voltage from the other end face. The entire cage has the role of
the cathode; the extractor acts as the anode, and an unnamed ring takes the role of the Wehnelt cylinder.
Most color cathode ray tubes — such as those used in color televisions — 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 red, green or blue phosphor to light up a color pixel on the screen. The resultant
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Electron gun - Wikipedia, the free encyclopedia
8/22/11 3:49 PM
color that is seen by the viewer will be a combination of these three primary colors.
Applications
The most common use of electron guns is in cathode ray tubes, which were widely used in computer and
television monitors. An electron gun can also be used to ionize particles by adding 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.
See also
Cathode ray tube
Electron microscope
Optics
Particle accelerators
References
External links
Howstuffworks.com: electron gun (http://electronics.howstuffworks.com/question694.htm)
Retrieved from "http://en.wikipedia.org/wiki/Electron_gun"
Categories: Electron beam | Particle accelerators | Vacuum tubes
This page was last modified on 20 August 2011 at 00:29.
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