Duoplasmatron
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The Duoplasmatron is an ion source in which a cathode filament emits electrons into a vacuum chamber. A gas such as argon is introduced in very small quantities into the chamber, where it becomes char
Prof. Dr. Manfred von Ardenne, June 1986
Hot cathode
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In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cat
A tungsten filament acting as a directly heated cathode in a low pressure mercury gas discharge lamp which emits electrons. To increase electron emission, a white thermionic emission mix coating is applied on hot cathodes, visible on the central portion of the coil. Typically made of a mixture of barium, strontium, and calcium oxides, the coating is sputtered away through normal use, eventually resulting in lamp failure.
Two indirectly heated cathodes (orange heater strip) in ECC83 dual triode tube
Glow of a directly heated cathode in an Eimac 4-1000A 1 kW power tetrode tube in a radio transmitter. Directly heated cathodes operate at higher temperatures and produce a brighter glow. The cathode is behind the other tube elements and not directly visible.
SEM Image of G1 Support and G1 Wire, of a heavily used Pentode showing Barium oxide Contamination (green) from the cathode.