accelerated is determined by the amplitude of the cavity signal. Electrons entering the space between the cavity
grids when the cavity signal is reversed are decelerated. Those electrons that are accelerated most will travel
farther toward the repeller plate before being turned back, while those that are decelerated most will be turned
back before getting close to the repeller plate. By now you probably realize that with the proper magnitude of the
cavity signal, Ea, and Er, the electrons will arrive in bunches.
a. The positions of the electrons in the tube at various times during their transit are shown in figure 7.
The zero distance position is midway between the cavity grids. Electrons at time A arrive when the cavity signal
is positive. These electrons are now accelerated and will travel farther before being turned back by the repeller
plate. Electrons at time B are unaffected because the cavity signal is zero. Electrons at time C are decelerated by
the cavity signal and are turned back after traveling a shorter distance. Notice how all of the electrons are
returned to the cavity grids at the same time.
Figure 7. Bunching action.
b. When the electrons are being returned by the repeller plate, the cavity signal again has an effect
on them. The electrons are no- traveling in the opposite direction and will be decelerated when
the cavity signal is positive.
The bunches of electrons that arrive back at the cavity grids are