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An electron gun is a component that produces an Electron Beam that has a precise Kinetic Energy , being used in Television s and Monitors which use Cathode Ray Tube technology, and in other instruments, as Electron Microscope s and Particle Accelerators . An 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 cathode and anode accelerates the electrons. A repulsive ring placed between them focuses the electrons onto a small spot on the anode on the expense of a lower extraction field strength on the cathode surface. Often at this spot is a hole, so that the electrons pass through the anode forming a collimated beam and are finally reach a second anode called a collector. This arrangement is similar to a Einzel Lens . Likewise one type of an Ion Gun consists of a cylinder, where gas enters from one end face, electron bombardment from the side walls, and an extraction voltage from the other end face. The cage has the role of the cathode, an extractor has the role of the anode, and an unnamed ring as the role of the Wehnelt cylinder. Most colour Cathode Ray Tubes - as those used in colour television - 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 colour dot of a Pixel of the screen, the resultant colour being a combination of these three. An Electron gun can be used to Ionise particles by adding or removing electrons from the Atom . This technology is sometimes used in Mass Spectrometry in a process called Electron Ionisation to ionise Vaporised or Gaseous particles. EXTERNAL LINK |
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