Re: [amsat-bb] Klystron info

[Bruce Bostwick <lihan161051@xxxxxxxxxxxxx>]

One clever idea I saw on Scientific American's Amateur Scientist column 
shortly before it was discontinued involved a molecular sorption pump.  
If you fill a Pyrex bottle with "molecular sieve", which is a highly 
porous material with a large amount of surface area per unit volume, 
frequently used in gas chromatography as a support or trap material, 
and heat it to drive off adsorbed gases and water vapor, it will have a 
HUGE capacity to trap air and any other gases that come in contact with 
it.  This is due to a non-classical behavior of gas molecules at low 
temperatures -- when they hit a surface, if that surface is colder than 
their 'condensation' or sorption temperature, they stick instead of 
bouncing off, and the gas pressure drops.

Seal the Pyrex bottle to whatever you want to evacuate, immerse the 
bottle in liquid nitrogen or a dry ice/acetone slurry (be EXTREMELY 
careful handling either!), and the cold will cause air and other gas 
molecules to stick to any surface they touch.  The enormous surface 
area of the molecular sieve in the bottle causes all the air arriving 
in the bottle to stick to the surfaces of the pores, drawing the part 
being evaculated down to a submicron vacuum.

Obviously, the part you're evacuating will need to be heated to 
*release* any gas molecules stuck to its interior surfaces, to avoid 
having them come loose later and spoil your vacuum.  The old tube 
manufacturers knew this .. commercially made tubes were baked almost 
red-hot in kilns while they were being pumped down.  You'll have to do 
the same, so be sure your internal parts are welded, not soldered, and 
make sure the mount can withstand the heat you have to apply to it.  
When it gets down to what you feel is a usable vacuum, seal the 
tubulation, flash the getter, and test your new tube ..

On Friday, Dec 27, 2002, at 14:58 US/Central, William Leijenaar wrote:

> I also like to know some (easy) ideas how to make enough vaccuum for a 
> Klystron.
> Ofcourse I am looking for KISS (Keep It Stupid Simple) amateur ideas 
> :-)
> I have some idea, but maybe someone else has a better one...
>
"Go ahead and do it, you can apologize later." -- RADM Grace Hopper, 
1906-1992
"The sunset is an illusion, but the beauty is real." -- Richard Bach

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