c. The diagram in figure 55 represents the
the input and output cavities. For this reason, a
same end view of the drift tube, and shows the path
klystron with internal cavities has less power loss at
of the beam electron in a cyclotron. The electron
higher frequencies.
actually spirals around the drift tube axis; and, at the
same time, it moves along the axis (length) of the
1-52.
NAMES OF THE KLYSTRON CAVITIES
drift tube.
a. Ordinarily, when you have to make
d. In addition to deflecting the beam
adjustments on the klystron, you cannot see the part
electrons away from the drift tube wall, the
of the klystron that your adjustment is affecting. For
cyclotron effect influences the electron density
example, when you have to tune each cavity, you
modulation (or bunching rate). Intervals between
don't ordinarily see the cavity itself; you only see a
bunches become shorter with increase in strength of
panel control that has a connecting link to the cavity.
stationary magnetic field lines.
These same
The panel control is identified by the name of the
magnetic lines determine the direction (clockwise or
cavity to which it connects.
counterclockwise) of the electrons' cycloidal motion.
b. The klystron may have from two to six
1-51.
EXTERNAL AND INTERNAL CAVITIES
cavities, but those most common in the field have
either three or four. Some of the klystron's cavities
Two types of resonant cavities are used with
(fig 56) have names that correspond to the functions
klystrons -- internal and external. Internal cavities
they perform. The first cavity is usually called the
are within the vacuum envelope of the tube.
"input cavity," no matter how many cavities may
External cavities are outside the vacuum envelope.
follow it. Similarly, the last cavity is referred to as
the "output cavity" because it transfers power to the
a. One advantage of external cavities is
output transmission line.
that they are easier to tune and maintain. They can
provide a tuning range twice that of internal cavities.
c. The cavity next to the output cavity is
External cavities, however, require a sealed ceramic
sometimes called the "penultimate cavity." The
window at each cavity and the windows cause
word penultimate means "next to the last."
considerable power loss at high frequencies.
d. The remaining cavities are referred to by
b. Internal cavities are totally within the
their position on the drift tube as "second cavity, "
vacuum envelope and windows are required at only
"third cavity," and so on.
Figure 56. Next-to-the-last cavity is called penultimate cavity.
344 L1
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