Radar System Engineering

330 THE MAGNETRON AND 1’HEPULSER [SEC. 103
magnetrons. The majority of existing magnetrons are of this type. A
variety of other designs have been constructed, most of which have not
proved to be as satisfactory as the strapped type. One type, however,
has several marked advantages over strapped tubes. It is known as the
“rising sun” magnetron (Figs. 10.9 and 1010). Mode separation is
accomplished in this design by making alternate resonators of a different
FIG. 10.10.—Cutaway view of rising-sunmagnetron with axial cathode. The wavelength
& 1,25cm. (Courtesv OJBell Telephone Laboratories.)
frequent y. It is interesting to note that this ‘resonant system results in
an operating or r-mode which lies intermediate in frequency between
other modes while, for strapped tubes, the r-mode has the lowest frequency.
For very high powers, the rising-sun system has considerable
promise. Unlike strapped systems, the rising-sun system permits the
anode to be made with a circumference and a length which are not small
compared to a wavelength without producing mode instabilities. Thus
even at high frequencies large cathodes and large emissions are possible.
10.3. Electron Orbits and the Space Charge.—An electron in the
interaction space of a magnetron is acted on by a constant magnetic field
parallel to the axis of the cathode, a constant radial electric field resulting
from the applied d-c potential, and the varying electric field extending
into the interaction space from charges concentrated near the ends of the