Mike, Attila, Rick,
> Which caesium beam standards were available in 1956?
The Atomichron, made by the National Company. This was the first
commercial cesium standard; about 50 were made. Attila, you saw one at
my house when you visited last year. It's about 7 feet tall. The one I
have was used by NBS(NIST), then made its way to a remote cabin in
Minnesota for a couple decades, then to a garage in Minneapolis, where I
bought it and drove it to Seattle. Atomichron photos here [1].
The hp 5060 and 5061 came much later.
> The picture of the beam tube is only a small fraction of the clock
itself. There are multiple racks full of RF equipment not shown
Correct. Better views of Essen's cesium clock and laboratory here [2].
Note also the Atomichron in the background of figure 6.
Since you are interested in the history of atomic clocks, especially
cesium beam clocks, I highly recommend these papers:
http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S01.pdf
"History of early atomic clocks"
Norman F Ramsey
http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S02.pdf
"Essen and the National Physical Laboratory’s atomic clock"
Dale Henderson
http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S04.pdf
"Atomic time-keeping from 1955 to the present"
Bernard Guinot, Elisa Felicitas Arias
http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_s05.pdf
"The classical caesium beam frequency standard: fifty years later"
Jacques Vanier, Claude Audoin
http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S10.pdf
"Fifty years of commercial caesium clocks"
Leonard S Cutler
The above come from:
https://iopscience.iop.org/issue/0026-1394/42/3
Special issue of Metrologia: “Special issue: fifty years of atomic
time-keeping: 1955 to 2005”,
Volume 42, Number 3, June 2005.
See also:
https://ieee-uffc.org/about-us/history/uffc-s-history/history-of-atomic-frequency-standards-a-trip-through-20th-century-physics/
"History of Atomic Frequency Standards: A Trip Through 20th Century Physics"
Arthur O. McCoubrey
https://ieee-uffc.org/about-us/history/uffc-s-history/atomichron/
"Atomichron: The Atomic Clock from Concept to Commercial Product"
Paul Forman
https://tycho.usno.navy.mil/ptti/1985papers/Vol%2017_01.pdf
The First Atomic Clock Program: NBS, 1947-1954
Paul Forman
A fine collection of clear photos and historical PDF here:
<https://ethw.org/Milestones:First_Atomic_Clock,_1948>
And finally,
https://nvlpubs.nist.gov/nistpubs/jres/122/jres.122.029.pdf
also found here: https://tf.nist.gov/general/pdf/2907.pdf
or here: https://tf.nist.gov/general/pdf/2917.pdf
"A Historical Review of U.S. Contributions to the Atomic Redefinition of
the SI Second in 1967"
Michael A. Lombardi
/tvb
[1] http://www.leapsecond.com/museum/nc2001/
[2]
https://www.researchgate.net/publication/320878080_Two_clocks_that_changed_the_world_The_birth_of_atomic_timekeeping
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