What is an amplifier of long range radar signals?

A traveling-wave tube (TWT) is an amplifier of long range radar signals. It is a vacuum tube that uses the interaction of an electron beam with a traveling electromagnetic wave to amplify the signal. The electron beam is focused into a narrow beam and passed through a slow-wave structure, which is a metal helix or a series of metal rings. The electromagnetic wave is propagated along the slow-wave structure, and the electron beam interacts with the wave, causing the wave to be amplified. The amplified wave is then extracted from the tube and used to amplify the radar signal.