Design features of the Stationary anode tube (pg168)
Glass envelope; made from borosilicate glass in order to stand high temperatures. Also acts as an electrical insulator between the negative cathode and positive anode. Contains the vaccum and supports the electrodes.
Vaccum; All air is excluded within the glass envelope. This prevents oxidation of the electrodes and acts as an electrical insulator. Also ensures that thermionic electrons moving across the tube do not collide with any gas atoms which would be ionized and reduce the kinetic energy of the thermionic electrons.
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