[time-nuts] COTS cesium standard physics package life
tmiller11147 at verizon.net
Thu Sep 29 18:37:42 EDT 2016
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
----- 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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