Figure 45. Only the input cavity of klystron has RF input.
Section III MULTICAVITY KLYSTRON AMPLIFIER
electric field because of the RF input as shown in
figure 45. The RF input power is much less than the
Figure 45 is a schematic diagram of a three-
dc power of the electron beam. This means that the
cavity klystron with its cavities arranged in cascade.
klystron's operation must begin with an interaction
The three resonant cavities are: the input cavity; the
between a very low power electric field and a high
middle or intermediate cavity; and, the output cavity.
power electron beam.
A cavity surrounds each of the three gaps along the
length of the drift tube, through which the electron
c. During the electric field and electron
beam flows. For the purpose of the following
beam interaction, the beam takes some RF energy
discussion, figure 45 represents the multicavity
from the electric field and the electric field, in turn,
takes some dc energy from the beam. Eventually,
the middle and output cavities also become sources
of electric fields through dc excitation (para 11) and
ARRANGEMENT OF CAVITIES
a similar interaction occurs between their electric
fields and the beam. Now, the electron beam
a. Like the cascade arrangement of
exchanges energy with electric fields of three
electron tube amplifiers, the multicavity klystron
cavities. The output cavity, however, delivers large
uses two or more resonant cavities in cascade to
amounts of RF power to the load. This is evidence
obtain an increase in power gain. The cascade
that the beam expends most of its energy in the
arrangement means that the cavities are situated such
output cavity. That is why we arrange the cavities in
that there will be a series of interactions between the
cascade, so that they can extract most of the energy
cavity electric (E) fields and the electron beam.
from the electron beam that flows through the drift
tube. The following paragraphs explain how the
b. The klystron begins the operation with
cavities take power from the electron beam.
the input cavity. The input cavity contains an