page_title: Electron gun
section_title: Characteristics
hierarchical_section_title: Electron gun / Characteristics
caption_attribution_description: English: Electron gun (cross section), part of a Traveling wave tube. Heater and Wires to heater Wehnelt cylinder, pierced shield and pierced angle Anode HV contact Electron beam exit Deutsch: Elektronenkanone einer Wanderfeldröhre Heizelement und Anschlussdrähte des Heizelementes Wehneltzylinder, gelochte Abschirmung und gelochtes Winkelblech Anode Hochspannungsanschluss Austrittsöffnung
context_page_description: An electron gun is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode ray tubes, used in nearly all television sets, computer displays and oscilloscopes that are not flat-panel displays. They are also used in field emission displays, which are essentially flat-panel displays made out of rows of extremely small cathode ray tubes. They are also used in microwave linear beam vacuum tubes such as klystrons, inductive output tubes, travelling wave tubes, and gyrotrons, as well as in scientific instruments such as electron microscopes and particle accelerators.
  Electron guns may be classified by the type of electric field generation, by emission mechanism, by focusing, or by the number of electrodes.
context_section_description: 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 to focus the electron beam (such as a Wehnelt cylinder), and one or more anode 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 an Einzel lens.
  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 color that is seen by the viewer will be a combination of these three primary colors.
caption: Electron gun from a travelling wave tube, cutaway through axis to show construction
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