Klystron tube

I found this in the museum at Croome Court. It is used to generate the high power radio waves for a radar device. It involves using an electron gun to fire a beam of electrons through two cavities. The first cavity is called the buncher and uses an oscillating electromagnetic wave to change the electric field between the sides of the cavity. The field oscillates very quickly, changing polarity. One way round it accelerates the electrons and then flips to decelerate electrons. Thus the electrons end up bunched rather than uniformly spread as they go on. They then enter the second cavity called the catcher. When the field in this acts against the motion of the electrons, the electrons do work on the field and give it energy, which amplifies the wave that was causing the field. By coupling the catcher back to the buncher, you can get it to generate a wave without any input by having it amplify the random noise that was in the circuit anyway. https://en.wikipedia.org/wiki/Klystron