Wehnelt cylinder
Encyclopedia
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 Rudolph Berthold Wehnelt
, a German physicist, who invented it during the years 1902 and 1903. A Wehnelt cylinder is also known as a grid cap, and plays the role of a control grid
. It is held biased to slight negative voltage relative to the cathode
(usually a hot cathode
). It has a shape of a hollow barrel with no top side (oriented towards the cathode) and a hole in the center of its bottom side (through which the focused electron beam escapes towards the anode).
Wehnelt cylinders are found in the electron guns of cathode ray tube
s and electron microscope
s, and in other applications where a thin, well-focused electron beam is required.
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
in the electron gun
Electron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
assembly of some thermionic
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 binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
devices, used for focusing and control of the electron beam. It is named after Arthur Rudolph Berthold Wehnelt
Arthur Wehnelt
Arthur Rudolph Berthold Wehnelt was a German physicist, noted for important contributions in the fields of X-ray physics, gas discharges and electron emission.-Life:...
, a German physicist, who invented it during the years 1902 and 1903. A Wehnelt cylinder is also known as a grid cap, and plays the role of a control grid
Control grid
The control grid is an electrode used in thermionic valves used to modulate the flow of electrons in the cathode to anode or plate circuit.- Operation :...
. It is held biased to slight negative voltage relative to the cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
(usually a hot cathode
Hot cathode
In vacuum tubes, a hot cathode is a cathode electrode which emits electrons due to thermionic emission. In the accelerator community, these are referred to as thermionic cathodes. The heating element is usually an electrical filament...
). It has a shape of a hollow barrel with no top side (oriented towards the cathode) and a hole in the center of its bottom side (through which the focused electron beam escapes towards the anode).
Wehnelt cylinders are found in the electron guns of cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s and electron microscope
Electron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...
s, and in other applications where a thin, well-focused electron beam is required.