English: Diagram of a traveling wave tube (TWT), showing how it works. A traveling wave tube is a specialized linear beam vacuum tube that amplifies microwaves (high frequency radio waves). It consists of an evacuated glass or ceramic tube with an electron gun at one end (left) that produces a high energy beam of electrons which is absorbed by a collector electrode at the other end.(right). The radio signal to be amplified is introduced by the input waveguide (left) and travels down the wire helix surrounding the electron beam. The microwaves absorb energy from the beam, and the amplified signal leaves through the output waveguide (right).