I think most of this, and a whole lot more concerning where the
development of the cavity magnetron lead, is in Robert Buderi's book,
"The Invention That Changed the World." Potentially very interesting
stuff for any techie.

In the last paragraph you quoted, there is what I consider a mistake
that can lead to misunderstanding of how things work. It suggests that
each cavity is an oscillator. The cavities are no more oscillators
than a bottle. Each is a resonator, whose resonance is excited by the
stream of electrons flying past, in much the same way as the bottle is
a Helmholz resonator which is excited by the stream of air flowing
past. In each case, what's going on in the resonator affects the
stream flowing by in a way that lets it further excite the resonator
synchronously with the resonant energy that's already there.

Cheers,
Tom

Richard Clark wrote:
Hi All,

Just a bit of RF history obtained from "Forty Years of Radio
Research," by George C. Southworth while I was doing some research for
a correspondent:

"As early as 1921, Dr. A.W. Hull of the General Electric Company
described the characteristics of a device which he called a
magnetron. It consisted of an axial filament surrounded by a
cylindrical plate between which a constant radial electric field
could be impressed. Superimposed on this arrangement and at right
angles to the electric field was an axial magnetic field.

... "Later the inductive load was reduced to a tiny Lecher frame.
A magnetron with this configuration was placed inside a small
waveguide by Dr. Harold S. Howe of the University of Michigan to
obtain a top frequency of nearly 50,000 mc. (1938).

"A few years earlier, 1934, Dr. Cleeton and Professor Williams
also of the University of Michigan had ... discovered a pronounced
absorption band for ammonia at about 27,300 mc. This ultimately
led to a new time-keeping device of high accuracy.

... "Finally the plate was made from a single block of copper with
appropriate segments milled inside its hollow periphery, each
representing an individual oscillator. This important step was
taken by physicists at the University of Birmingham in the late
thirties. They also applied plate power in short pulses and at
much higher levels than had been used previously. This was not
only more appropriate for good magnetron operation but it
provided an almost ideal signal for radar use. ... Details of this
device were brought to America first by Sir Robert Watson-Watt and
Drs. Cockcroft and Bowen in September, 1940."

73's
Richard Clark, KB7QHC