Rubidium cells with a side arm run the side arm at a lower temperature.
Then the excess rubidium condenses in the side arm.
The vapour pressure in the cell then becomes that vapour pressure that
exists over the solid rubidium in the side arm. If the pressure
rises, more will deposit in the side arm.
If some is lost/absorbed by walls, then some of the solid sublimes to
make a more vapour.
By controlling the temperature of the side arm you control the
pressure in the lamp.
Side arm temperature may be just due to design, i.e. half way between
the heated cell
and the circuit board temperature.
I have only played with an LPRO which has no side arm and so no
reserve rubidium.
It has only just enough to make the desired pressure. I think the
cells with side arms are neat,
you should never run out of gas, and there is always the possibility
if elevating/depressing
the pressure by by changing the side arm temperature.
cheers, Neville Michie
On 20/01/2011, at 6:55 AM, Magnus Danielson wrote:
On 01/19/2011 06:44 PM, Poul-Henning Kamp wrote:
In message<dbb70463b9d04f6589fbf97b2e4be...@vectron.com>, "Bob
Camp" writes:
Conventional gas cells have a finite lifetime on the
lamp.
It used to be that Rb's would fail lock because the bulb dimmed
from Rb
absorption into the glass, but I think they got that fixed with a
teflon
coating.
Thes days most of them ultimately fail from the high operating
temperature,
through a variety of mechanisms.
For the CSAC, my bet would be that the laser is the limiting factor.
I agree, for the CSAC I would expect that the laser would slowly
dim, especially as it sits within the oven. Not optimum to keep the
junction temperature down.
For my older Rubidium, the Rubidium lamp had splattered the
Rubidium. When I heated it the first time I did get a dimmed glass,
but heating it again orienting it properly (so hot gas rising into
the back where I wanted it) I resolved the problem... within
minutes. So I really wonder if it absorbs into the glass.
Exactly why splattered rubidium cause a problem for the rubidium
lamp I am not 100% sure about, but my guess is that maybe it will
expose too large area and thus causing too large gas-pressure to
let the RF-field light up the gas. If someone who actually know
could explain it, I would be happy to learn.
Cheers,
Magnus
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