Electron gun

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Electron gun from a cathode-ray tube
Vidicon video camera tube

An electron gun (also called electron emitter) is an electrical component in some

electron beam that has a precise kinetic energy
.

The largest use is in

particle accelerators
.

Electron guns may be classified by the type of electric field generation (DC or RF), by emission mechanism (thermionic, photocathode, cold emission, plasmas source), by focusing (pure electrostatic or with magnetic fields), or by the number of electrodes.

Design

Electron gun from an oscilloscope CRT
Setup of an electron gun. 1. Hot cathode. 2. Wehnelt cylinder. 3. Anode

A direct current, electrostatic thermionic electron gun is formed from several parts: a

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
.

An RF electron gun[1] consists of a Microwave cavity, either single cell or multi-cell, and a cathode. In order to obtain a smaller beam emittance at a given beam current, a photocathode is used.[2] An RF electron gun with a photocathode is called a photoinjector.

A photoinjector based on a "one and a half cells" microwave cavity at a frequency of 2856 MHz.

Photoinjectors play a leading role in X-ray Free-electron lasers and small beam emittance accelerator physics facilities.

Applications

Schottky-emitter electron source of an electron microscope

The most common use of electron guns is in

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
.

An

gaseous particles. More powerful electron guns are used for welding, metal coating, 3D metal printers
, metal powder production and vacuum furnaces.

Electron guns are also used in medical applications to produce

X-rays
.

Electron guns are also used in

travelling-wave tube amplifiers for microwave frequencies.[3]

Measurement and detection

travelling-wave tube
, cutaway through axis to show construction

A

nanocoulombmeter in combination with a Faraday cup can be used to detect and measure the beams emitted from electron gun and ion guns
.

Another way to detect electron beams from an electron gun is by using a phosphor screen which will glow when struck by an electron.

See also

References

  1. ^ H.G. Kirk, R. Miller, D. Yeremian, Electron guns and pre-injectors, pp. 99-103, in A. W. Chao and M. Tigner, Editors, "Accelerator Physics and Engineering" World Scientific, Singapore, 1998
  2. ^ I. Ben-Zvi, photoinjectors, pp. 158-175, in A. W. Chao, H.O. Moser and Z. Zhao, Editors, "Accelerator Physics and Technology Applications" World Scientific, Singapore, 2004
  3. S2CID 36963575
    .
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