Hairpin cathode
A hairpin cathode or filament is the part of the electron source in electron microscopes that supplies the electrons .
It consists of a U-shaped bent wire (usually tungsten ), which is made to glow with the help of an electric current in a vacuum (see hot cathode ). The electron cloud emerging from the wire is accelerated by the anode voltage in the direction of the anode and passes the anode screen as a thin electron beam . The intensity of the electron beam can be controlled with a Wehnelt diaphragm or a Wehnelt cylinder .
Hairpin cathodes become thinner and thinner during operation due to the evaporation of tungsten and burn out after a while. They are therefore wearing parts and are offered ready-made for various electron microscopes.
literature
Winkler, O., Thermionic hairpin cathode, European patent application EP 0 287 774 A2, October 26, 1988 https://data.epo.org/publication-server/html-document?PN=EP0287774%20EP%200287774&iDocId=3864645