[time-nuts] Maser info (vacuum levels)
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)..
>> 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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