The klystron

A klystron is the linear-beam electron tube. It has electron gun, one or more cavities, and a device which modulates the electron beam. There are different types of klystron tube. The most common are multicavity and reflex klystrons.A multicavity klystron is shown in the figure given below. In first cavity, the electron beam is velocity modulated. This means that speeds of electrons are made to increase and decrease alternately at the rapid rate. This causes density of electrons in beam to change as beam moves through subsequent cavities. The intermediate cavities increase magnitude of electron beam modulation, resulting in the amplification. The output is taken from last cavity. Peak power levels in some multicavity klystrons can exceed 1 MW.

A reflex klystron has one cavity only. A retarding field causes electron beam to periodically reverse in the direction. This produces a phase reversal which allows large amounts of energy to be drawn from electrons. The reflex klystron generates low-power UHF and microwave signals, on order of a few watts.

                                                                             Figure---A multicavity klystron.