Figure 49. Applegate diagram showing beam electrons velocity and density modulation.

c. Now refer to figure 49 and notice that

(2) A short time after electron number

the diagonal lines are numbered 1, 2, and 3. For the

1, electron number 2 passes the first gap, and then

purpose of this explanation let's assume that these

the second gap. However, electron number 2 passes

lines are electron paths. As shown, all three lines

each gap at a time when the cavity RF voltage is

have equal slopes (parallel to each other) until they

zero.

reach the input cavity waveform. This indicates that

(3) Exactly one-half cycle after electron

all three electrons have equal velocities until they

number 1, electron number 3 passes the first and

reach the first gap, as follows.

second gaps. Notice that at this time both cavity RF

(1) Electron number 1 passes the first

voltages are positive. Electron number 3, therefore,

gap when the input cavity RF voltage is negative,

accelerates at each gap crossing. This acceleration is

electron number 1 surrenders a portion of its energy

indicated by the upward bends in line number 3

to the input cavity. This causes the velocity of the

where it crosses the input and middle cavity

electron to decrease. This deceleration is indicated

waveforms.

by a decrease in the slope of line 1 where it crosses

d. Although each electron enters the

the input cavity waveform. Electron number 1

drift tube at a different time, all three

continues through the middle cavity at a time when

electrons reach the output cavity at the same

the RF voltage is negative. This negative voltage

causes electron number 1 to lose additional energy

and further deceleration.