Hot cathode

（重定向自Cathode heater）

A tungsten filament in a low pressure mercury gas discharge lamp which emits electrons. To increase electron emission a white thermionic emission mix coating is applied, 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, often eventually resulting in lamp failure.

Two indirectly-heated cathodes (orange heater strip) in ECC83 dual triode tubeCutaway view of a triode vacuum tube with an indirectly-heated cathode (orange tube), showing the heater element inside

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.

In vacuum tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. The heating element is usually an electrical filament, heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment and do not require heating. There are two types of hot cathode. In a directly-heated cathode, the filament is the cathode and emits the electrons. In an indirectly-heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.

单词	Cathode heater
释义	Cathode heater 英语百科 Hot cathode （重定向自Cathode heater） In vacuum tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. The heating element is usually an electrical filament, heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment and do not require heating. There are two types of hot cathode. In a directly-heated cathode, the filament is the cathode and emits the electrons. In an indirectly-heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.
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