Electron gun

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 televisions and monitors which use cathode ray tube technology, as well as in other instruments, such as electron microscopes 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, 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 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.

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 where the electrons will impinge upon either a 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.

Applications

An electron gun can 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.