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Electron gun

 
Electron Gun

 
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Electron gun
 
 
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An electron gun (also called electron emitter) is an electrical component that produces an electron beam that has a precise kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 and is most often used in television
Television

Television is a widely used telecommunication mass-media for transmitting and receiving moving , either monochrome or color, usually accompanied by sound....
s and monitors
Computer display

A visual display unit, often called simply a monitor or display, is a piece of electrical equipment which displays images generated from the video output of devices such as computers, without producing a permanent record....
 which use cathode ray tube
Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen....
 technology, as well as in other instruments, such as electron microscope
Electron microscope

An electron microscope is a type of microscope that uses a particle beam of electrons to illuminate a specimen and create a highly-magnified image....
s and particle accelerators. Electron guns may be classified in several ways:

, electrostatic thermionic electron gun is formed of several parts: a hot cathode
Hot cathode

In vacuum tubes, a hot cathode is a cathode electrode which emits electrons due to thermionic emission. The heating element is usually an electrical filament....
, which is heated to create a stream of electrons via thermionic emission
Thermionic emission

Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the forces restraining it....
, electrodes generating an electric field
Electric field

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field ....
 which focus the beam—such as a Wehnelt cylinder
Wehnelt cylinder

A Wehnelt cylinder is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. It is named after Arthur Wehnelt, a German physicist, who invented it during the years 1902 and 1903....
—and one or more anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 electrodes which accelerate and further focus the electrons.






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Encyclopedia


Egun
An electron gun (also called electron emitter) is an electrical component that produces an electron beam that has a precise kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 and is most often used in television
Television

Television is a widely used telecommunication mass-media for transmitting and receiving moving , either monochrome or color, usually accompanied by sound....
s and monitors
Computer display

A visual display unit, often called simply a monitor or display, is a piece of electrical equipment which displays images generated from the video output of devices such as computers, without producing a permanent record....
 which use cathode ray tube
Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen....
 technology, as well as in other instruments, such as electron microscope
Electron microscope

An electron microscope is a type of microscope that uses a particle beam of electrons to illuminate a specimen and create a highly-magnified image....
s and particle accelerators. Electron guns may be classified in several ways:
  • 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.


Characteristics

A DC, electrostatic thermionic electron gun is formed of several parts: a hot cathode
Hot cathode

In vacuum tubes, a hot cathode is a cathode electrode which emits electrons due to thermionic emission. The heating element is usually an electrical filament....
, which is heated to create a stream of electrons via thermionic emission
Thermionic emission

Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the forces restraining it....
, electrodes generating an electric field
Electric field

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field ....
 which focus the beam—such as a Wehnelt cylinder
Wehnelt cylinder

A Wehnelt cylinder is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. It is named after Arthur Wehnelt, a German physicist, who invented it during the years 1902 and 1903....
—and one or more anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 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
Einzel lens

The Einzel lens is used in ion optics to focus ions in flight and is accomplished through manipulation of the electric field in the path of the ions....
.

An ion gun
Ion source

An ion source is an electro-magnetic device that is used to create Ion. These are used primarily within Mass spectrometry, particle accelerators, Ion implantation and Ion thruster....
 consists of a cylinder, where gas enters from one end face, undergoes electron bombardment from the side walls, and an 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
Wehnelt cylinder

A Wehnelt cylinder is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. It is named after Arthur Wehnelt, a German physicist, who invented it during the years 1902 and 1903....
.

Most color cathode ray tubes— such as those used in color televisions - are made up of three electron guns, each one producing a different stream of electrons. Each stream travels through a shadow mask
Shadow mask

The shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images ....
 where the electrons will impinge upon either a red, green or blue phosphor
Phosphor

A phosphor is a substance that exhibits the optical phenomenon of phosphorescence .Phosphors are transition metal compounds or rare earth element compounds of various types....
 to light up a color pixel
Pixel

In digital imaging, a pixel is the smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots, squares, or rectangles....
 on the screen. The resultant color that is seen by the viewer will be a combination of these three.

Applications

An electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
 gun can be used to ionize particles by adding or removing electrons from an atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
. This technology is sometimes used in mass spectrometry
Mass spectrometry

Mass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds....
 in a process called electron ionization
Electron ionization

Electron ionization is an ionization method in which energetic electrons interact with gas phase atoms or molecules to produce ions. The technique widely used in mass spectrometry, particularly for organic chemistry molecules....
 to ionize vaporized or gaseous particles.

External links

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See also

  • Cathode ray tube
    Cathode ray tube

    The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen....
  • electron microscope
    Electron microscope

    An electron microscope is a type of microscope that uses a particle beam of electrons to illuminate a specimen and create a highly-magnified image....
  • Optics
    Optics

    Optics is the study of the behavior and properties of light including its optical phenomena with matter and its imaging by optical instruments....
  • Particle accelerators