[time-nuts] Symmetricon CS question

Magnus Danielson magnus at rubidium.dyndns.org
Fri Jun 24 11:46:44 UTC 2011

On 06/24/2011 07:39 AM, Perry Sandeen wrote:
> List,
> I’m still confused about the new Symmetricon CS unit.  Is it truly a cesium primary standard or is it a secondary standard that happens to use cesium?
> IF it is truly a primary standard, is saving up the $1500 for one a better deal IN THE LONG RUN than getting a used HP or other brand C.S. unit?   I’d want to use it and not have to fiddle with it to keep it running.
> Again, opinions welcomed

The CSAC is a secondary standard. It just happens to use Caesium.

A primary standard has a very high degree of repeatability in them, so 
that systematic bias effects can be made very very small. This is not as 
such connected to the atom being used as much as the technology being 
used. A gas cell standard such as the rubidium gas cell, has systematic 
pulling effects. Using temperature stabilization this pulling can be 
stabilized, but there is no real method of within the standard detect 
and compensate this pulling. Even the high quality beam of 5071 has 
systematic effects, but engineered way down.

The CSAC is a caesium gas cell. It avoids some of the typical rubidium 
gas cell issues by providing a significantly different physical package 
design. It does not have an RF resonator chamber for instance, which 
detuning from resonance causes a pulling effect. It has polarization 
control to avoid that pulling effect (specific to laser excitation 
rather than the non-coherent rubidium-lamp of normal optically pumped 
rubidium cells) etc. Control-loops to stabilize various effects to 
achieve a stable pulling.

But it is not a primary reference, rather it is a small sized and power 
efficient secondary reference. If you view it like that, then you can 
appreciate it for what it is and use it in the proper applications.

I like it and would like to try it out, but it will not replace a real 
caesium beam by far.


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