[time-nuts] Rb lamp lifetime...

Adrian rfnuts at arcor.de
Mon Nov 3 00:46:37 UTC 2008


Hello,

there are some interesting hints (including lamp rejuvenation) in the 
attached papaer that was posted here a few months ago by Gerald 
Molenkamp VK3FGJM.

Regards,
Adrian


Yuri Ostry schrieb:
> Hello,
>
> Readed list archives and googled a lot, and seen two opposing points of
> view - one is that there is nothing to age in Rb lamp, another is that
> Rb lamp is degrading when in operation (without details, how and why).
>
> I'm planning to get some Efratom Rb oscillator to use it in a
> constantly running home lab frequency reference. Trying to understand
> for myself, is it worth to get spare unit (or even two) of the same
> model just to have replacement lamp on hand.
>
> One more question - does someone seen Rb standard that is
> malfunctioned due to degraded lamp, that, at same time, does have
> good vacuum. If so, which model, and how the failed lamp looks like?
> Was there any attempts to "rejuvenate" the lamp? (for example, heating
> to remove glass darkening, if any, or similar experiments).
>
> By the way, I'm very curious about physical process that may cause
> lamp degradation.
>
> Rubidium-87 that is included in the lamp (according to
> manuals) is a radionuclide, beta emitter. It decays very slowly (4.7
> billion years half life) to stable Strontium-87, emitting 282.62keV
> electrons and (anti?)neutrino. I don't think that 87Rb decay may
> interfere with unit operation after tens of years, unless 87Sr is
> "poisonous" so much so it can interfere with lamp operation even in
> tiniest amounts. 
>
> The only reference I located to date, is following article, that is
> not available to general public. It is hard to understand for me just
> from this abstract, does it specifically related to space environment
> factors, or it is something that may cause degradation of Rb clocks
> that is operated in average lab on Earth. ;)
>
>   
>> A Mechanism of Rubidium Atomic Clock Degradation: Ring-Mode to
>> Red-Mode Transition in rf-Discharge Lamps 
>> Camparo, J.   Mackay, R.   
>> Aerosp. Corp., El Segundo;
>>
>>
>> This paper appears in: Frequency Control Symposium, 2007 Joint with
>> the 21st European Frequency and Time Forum. IEEE International 
>> Publication Date: May 29 2007-June 1 2007
>> On page(s): 45-48
>> Location: Geneva, 
>> ISSN: 1075-6787
>> ISBN: 978-1-4244-0647-0
>> INSPEC Accession Number: 9805223
>> Digital Object Identifier: 10.1109/FREQ.2007.4319027
>> Current Version Published: 2007-10-01 
>>
>>  
>>  
>>  
>>  
>> Abstract
>> In the vapor-cell atomic clock, long-term stability can be
>> influenced by slow variations in the discharge lamp's output via the
>> light-shift effect. Additionally, over a multi-year mission lifetime
>> the lamp's aging can degrade its optical pumping efficiency.
>> Understanding the mechanism(s) that drives these changes is
>> particularly important for spacecraft devices, where the atomic
>> clocks are called upon to function continuously and reliably for
>> many years. Here, we consider the two well-known, but little
>> studied, modes associated with alkali rf-discharge lamp operation:
>> the ring mode and the red mode. Consistent with previous research,
>> we find that the ring mode is best for optical pumping, and that the
>> clock-signal amplitude degrades significantly when the lamp operates
>> in the red mode. Examining the emission spectrum as the lamp
>> transitions between these two modes, we show that the ring-mode to
>> red-mode transition is driven by radiation trapping within the lamp.
>>     
>
>
>   

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