[time-nuts] CBT EOL

[Dave Carlson]

Hello,

Speaking not from a physicist perspective, but from being in the business 
for over 20 years...

The mechanism depends somewhat on the amount of flux that has been traveling 
through the CBT, which determines if the cesium becomes exhausted before the 
electron multiplier first dynoe "wears out".

In general with the HP/Agilent/Symmetricom CBT there is enough getter 
material inside to trap contaminants well beyond the time that the cesium 
should run out in the oven. As long as the Ion Pump is working, internal 
contamination should be the minimal contributor to EOL.

Whether the cesium runs out or the Electron Multiplier first dynode loses 
its coating is largely dependent on the amount of flux. The High-Performance 
CBT run at a hotter oven temperature to gain better S/N and thereby exhaust 
the available cesium at a faster rate. In these CBT the EOL mechanism is 
more likely due to that. As the cesium runs out the S/N degrades. Increasing 
the EM voltage can help, but eventually you're amplifying more and more 
noise.

In the standard-performance or long-life CBT the EOL mechanism is more 
likely due to the first dynode of the EM becoming depleted of its coating, 
than buildup of internal contaminants.

Dave

----- Original Message ----- 
From: <wa1zms at att.net>
To: <time-nuts at febo.com>
Sent: Monday, February 04, 2008 6:39 AM
Subject: [time-nuts] CBT EOL


When a CBT reaches end-of-life, is it because the source of Cs is used
up? Or is it due to contamination of the electron multiplier?

I've heard both as causes but wanted more info.

I have a CBT with very low beam current and it keeps falling. I'm wondering
if running a higher than normal EM voltage might help keep it on 
life-support.

-Brain, WA1ZMS/4

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