Radar System Engineering

SEC. 103] ELECTRON ORBITS AND THE SPACE CHARGE 333
charge. The fields in a magnetron, however, are certainly such as to
produce this separation of fast and slow electrons.
The problem is shown in more detail in Fig. 10.13. Consider an
electron at point A at the instant for which the fields are as shown. The
r-f field at this point tends to speed Up the electron. As it speeds up, the
radius of curvature of its path is decreased, and it will move along a path
corresponding to the solid line and strike the cathode with appreciable
energy. This electron is thus removed from the space charge, and plays
no further role in the process except perhaps to produce a few secondary
electrons from the cathode. An electron at point 1?, however, is in a
decelerating r-f electric field. AS a result of the reduction in electron
velocity, the radius of curvature of its path is increased. If the frequency
of oscillation is appropriate, this electron will always be in a
decelerating field as it passes before successive anode segments. The
result is that the electron, following a path of the type shown, eventually
strikes the anode. Because of retardation by the r-f field, the electron
gives up to the r-f field the energy gained in its fall through the d-c field
to the anode.
Since the electron moves from the cathode to the anode in a very
small number of oscillations, the condition that the electron keep step,