[time-nuts] COTS cesium standard physics package life

Tom Miller tmiller11147 at verizon.net
Thu Sep 29 18:37:42 EDT 2016

Hi John,

I have a Datum FTS-5060 unit. Did you just open up the heater line to the 
beam tube? I like the idea of conserving the Cs when pumping down the tube 
for maintenance.


----- Original Message ----- 
From: "John Miles" <john at miles.io>
To: "'Discussion of precise time and frequency measurement'" 
<time-nuts at febo.com>
Sent: Thursday, September 29, 2016 6:05 PM
Subject: Re: [time-nuts] COTS cesium standard physics package life

>> 1.  Cesium depletion, which only occurs when the tube is operating with
>> cesium oven on, and high voltage at the other end; and
> The Cs atoms need to be electrically neutral, so their depletion rate 
> shouldn't depend on the presence of HV, just the oven heater.  State 
> selection wouldn't work on ionized atoms, and you also wouldn't want them 
> to be accelerated towards the electron multiplier until after they've 
> reached the ionizer filament at the end of the cavity.  (The longer they 
> spend hanging out with Schroedinger's cat in the Ramsey cavity, the 
> narrower the line width.)
>> 2.  Tube vacuum and other physical aspects that may deteriorate over
>> time, whether or not the tube is operating.  The routine ion pumping
>> helps keep the vacuum up in storage, but is not as effective as the
>> continuous pumping that occurs during operation.
> Some of the HP standards (5060, 5061, 5071) have a CS OFF setting that 
> enables the ion pump by itself.  Those tubes should last indefinitely in 
> that mode of operation.  Unfortunately the 5062C didn't have a way to 
> disable the Cs oven while leaving the ion pump active, which is probably 
> why there are so few operational 5062C tubes left.  By now, most are 
> either out of cesium or too gassy for the ion pump to recover.
> I added a switch to  my 5062C to allow the vacuum to be maintained without 
> running  the Cs oven.  It gets turned on every so often, maybe a couple of 
> times per year, when I want a noisy signal source with known ADEV 
> characteristics.  Even though the ion pump runs 24/7/365, there are always 
> a few overcurrent cycles on initial powerup for some reason, where the 
> beam current exceeds the trip point and shuts down the power supplies. 
> Something inside the tube is apparently outgassing during warmup --  
> whether it's the Cs oven or the hot-wire ionizer ribbon, I don't know. 
> But the condition always clears itself within a few  seconds.  The same 
> thing happens when I turn my 5061s on after a long period in CS OFF.
> - john, KE5FX
> Miles Design LLC
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