The electrons that make up the beam are emitted from a heated cathode filament.
2.
The cathode filaments are still used for protection of the ballast from overheating if the lamp does not ignite.
3.
Each tube in a VFD has a phosphor coated anode that is bombarded by electrons emitted from the cathode filament.
4.
A negatively biased Wehnelt electrode positioned between the cathode filament and anode applies a small electric field, which focuses the electrons as they pass through the anode.
5.
Hot-cathode, gas discharge tubes such as the thyratron may also achieve similar levels of efficiency but heated cathode filaments are delicate and have a short operating life when used at high current.
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