[time-nuts] Maser info (vacuum levels)

Heathkid heathkid at heathkid.com
Fri Sep 3 04:49:29 UTC 2010

Sounds like the parts of a "salvaged" SEM would be a good start for a 
project such as this (assuming the diffusion pump is included - I've been 
looking for one for a while but it seems the pumps are almost *always* 
missing).  But still, if you could find one locally (freight is $$$) there 
are a lot of very good, high precision parts just begging to be "hacked".

----- Original Message ----- 
From: "jimlux" <jimlux at earthlink.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, September 03, 2010 12:34 AM
Subject: Re: [time-nuts] Maser info (vacuum levels)

> Mark J. Blair wrote:
>> On Sep 2, 2010, at 10:28 AM, Corby Dawson wrote:
>>> This EFOS maser typically runs with the two vacuum pressures below
>>> 1.5 X 10-6 Torr. (as measured via the ion pump current)
>>> Maximum should not exceed about 3.6 X 10-6 Torr for either pump.
>>> The internal vacuum will drop to about 1 X10-7 Torr if the Hydrogen
>>> to the disassociator is turned off.
>> Back in college, I took a semiconductor device physics course which
>> included a lab where we made simple ICs (the most complex devices
>> were SR latches). We had a vapor deposition system for plating on
>> gold or aluminum, which pumped the chamber down below 10E-12 Torr
> maybe 1E-6 micron (1E-9 torr)..
>  as
>> I recall, within ten minutes or so after a clueless freshman opened
>> the beast up and tossed in a bit of aluminum or gold wire and a few
>> chunks of silicon with their grubby hands (ok, we used tweezers, but
>> still...). The whole unit was about as big as a refrigerator or two.
>> It used a rotary-vane roughing pump and an oil diffusion pump with a
>> liquid nitrogen trap. This was about 25 years ago.
> Sounds about right.. the mechanical pump will pull it down to a few 
> microns in a minute or so (I assume it's like a bell jar with maybe 50 
> liters total volume?)
> Another 10 minues on the diff pump (probably something like a 4" throat.. 
> with a LN2 trap)..
> As long as you don't forget to close the High vacuum gate valve before 
> venting the chamber, very reasonable.
>> Reading here about the troubles of pulling a very good vacuum, I'm
>> now wondering what sorts of painful engineering went into making the
>> machine turn-key and freshman-proof? It's entirely possible that I've
>> mis-remembered the pressure level, but that's the exponent that stuck
>> in my mind for whatever reason.
> Lots of interlocks to keep you from doing dumb stuff (e.g. venting to 
> atmosphere with the diff pump hot and connected), actually not all that 
> dirty.. you probably weren't sticking complex mechanical stuff in there.. 
> basically a wafer that you'd put next to the evaporator source. So no 
> issues with virtual leaks, etc.
> At work, we've got tons (well, tens) of these little evaporation 
> workstation things.. A rolling cart about a meter by half a meter, and a 
> meter high, with a bell jar on top.  A mechanical two stage pump and a 3" 
> diff pump under the plate.  A couple of feedthroughs for current to heat 
> the evaporation source.  A couple toggle switches, a ion and a 
> thermocouple gage..  We don't use the for evaporating metal (at least I 
> and the folks in my section don't)... we use them to test electronics 
> under vacuum..
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