[time-nuts] chip scale atomic clock

Magnus Danielson magnus at rubidium.dyndns.org
Wed Dec 30 02:25:03 UTC 2009


Peter Vince wrote:
> 2009/12/26 Robert Lutwak <Lutwak at alum.mit.edu>:
>> ...
>> CSAC is intended for portable battery-powered operation. Surely your
>> basement has the space and wallplug power to support an LPRO. (p.s. don't
>> cool the damn thing, heat it).
>> ...
> 
> Hi Robert,
> 
>      Do I understand you are suggesting heating an LPRO, not cooling
> it?  That seems to go against what I understood, that greater cooling
> leads to increased life.

While not directed to me, these are my understandings:

Besides the power applied to heat the Rb lamp, the physical package 
needs to be at the sweet-spot in temperature, so heating is performed.

By lowering the cooling of the physical package, the powerconsumption 
goes down. So better isolation has to cool of less effect.

This stands in contradiction to the lifetime of the electronics, but the 
physical package and electronics have two different requirements.

>      As an aside, a newbie question if I may: being so used to Caesium
> standards being THE reference, I was surprised to hear that the CSAC
> has an aging mechanism - can you say a few words to explain that
> please?

Don't confuse the stability and repeatability of elaborate beam clocks 
with that of (cheaper) gas cell clocks. Rubidium and Thallium beams has 
existed but Cesium was a better match for that purpose, Rubidium was 
found more suitable for the simpler and cheaper gas cell standard. 
Rubidium excells over Cesium in laser cooled fointains, since it reacts 
better to the laser cooling. Thus, each technology finds different 
technological balances with different atoms.

May one suspect that the gas cells buffert gas mixture and resulting 
wall-shift/gas-shift balance is one of the long-term age effects, just 
as with ordinary rubidium gas cells. Another aspect to consider is that 
this clock does not have the C-field servo loop which modern cesium 
beams have.

Then again, I think Robert can lecture a mere student (lazy such) to the 
field like me.

Cheers,
Magnus



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