Figure 31. Functional sections of multicavity klystron.
b. Figure 31 shows a typical klystron
b. The combined effects of the curvature of
divided into its three functional sections: the electron
the cathode disc, the focus electrode, and the
gun, the RF section and the collector. We will
modulating anode give an overall effect of an
discuss the function of each section in the following
electrostatic lens within the electronic gun. The
paragraphs.
electrostatic lens focuses the electron beam into the
first drift tube section.
1-35.
FUNCTION OF THE ELECTRON GUN
a. The electron gun (fig 32) is the source
of an electron stream. The action of the electron gun
causes electron acceleration and focusing because of
the way it's constructed. This is what happens.
(1) The heated CATHODE emits
electrons. The amount of electron acceleration is
due, in part, to the filament (heater) that heats the
cathode. The cathode's emitting surface is concave.
This causes the electron trajectories and helps to
focus the electron stream into a narrow beam.
(2) A cylindrical FOCUS electrode
surrounds the cathode. The focus electrode is kept
either at cathode potential or at some negative
potential with respect to the cathode. This causes a
squeezing effect on the electron stream to focus the
stream into a narrow beam along the axis.
(3) The cup-shaped MODULATING
anode provides a "funnel" through which the
electrons flow. The modulating anode potential is
positive with respect to the cathode, and therefore
causes the electrons to flow away from the cathode
Figure 32. Simplified view of electron gun.
toward the anode itself.
344 L1
35
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