Bunching Effect & Transfer of Energy in a Travelling Wave Tube?

Question

Pls Explain the exact process in which the Density/Velocity Modulation takes place in a TWTand how exactly is the Amplification takes place at the level of electrons. Kindly explain in simple language.

Answer 1

A microwave signal goes down a coiled conductor that wraps around a long tube with an electron beam traveling through it. As the microwaves travel down the tube, they have both positive and negative peaks which attract and repel the electron beam. This causes them to bunch together. eventually they come to a resonant collector where they are collected. The net result is that there is amplification.

http://en.wikipedia.org/wiki/Travelling_wave_tube