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Re: [TCML] x-ray transformer for Tesla supply




-----Original Message-----
>From: David Rieben <drieben@xxxxxxxxxxx>
>Sent: Dec 6, 2007 7:56 PM
>To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
>Cc: David Rieben <drieben@xxxxxxxxxxxxxxx>
>Subject: Re: [TCML] x-ray transformer for Tesla supply
>
>Hi Rich,
>
>LOL, yes, I figured that you didn't personally own such a vacuum
>chamber but I was still amazed at the prospect of a high vacuum
>chamber of that magnitude, even in a commercial/industrial setting.
>Must have taken a good while to pump it down ;^)

We're getting a bit OT, here, but since we actually do high voltage breakdown testing in it, the mods will probably let is slide...

At Jet Propulsion Lab we have one of the largest bell jars in the world.. 6 ft across. It's in a anechoic chamber and used for high power breakdown testing of antennas and RF components in both hard vacuum, and at low pressures in air or Mars gas.  The throat to the big diffusion pump is about 2-3 ft in diameter and there's a large pneumatically actuated gate valve that size to close it off. 

It pumps down pretty fast (minutes).. we backfill with Mars gas (mostly CO2 and Argon) to a few torr for breakdown testing for things like the rovers.  I haven't run a tesla coil in the chamber yet (I'm afraid that a streamer might damage the bell jar, and there would be a heap of explaining to do...) but we've done lots of other things at, say, 400 MHz and higher.

We also have a bunch of more conventional vacuum chambers of various sizes (25' diameter, 10' and smaller) with stuff to simulate solar radiation and cold space (many truckloads of liquid nitrogen into radiators around the inside of the chamber).

I think Johnson Space Center in Houston has a really big chamber too.

20-30 ft chambers are actually fairly common. Anyone in the satellite business would have one.  

There's a huge chamber at the White Sands Test Facility for testing rocket motors in vacuum.  It has enormous steam ejectors as part of the pumping system.  I think that Glenn Research Center has a similar capability. (they also have a drop tower some 500 ft deep that can be pumped down to eliminate air drag)

And 5-10 ft chambers are also quite common for things like evaporating metal or degassing potting material. How do you think they put that shiny coating on those sunglasses?  Many, many, many pairs go into a BIG vacuum chamber and they evaporate the metal onto them.

These big chambers are an area where the diffusion pump still reigns.. For smaller chambers, the turbos and ion pumps are more popular, because they're oil free, but making a 48" turbo pump would be a pretty big chore.


>> Please let me set it straight, I do not have a chamber like that. The
>> chambers were in the lab complex where I worked. The 30 foot one was used 
>> to
>> do testing on the Mercury and Gemini spacecraft. The large chamber was in
>> mothballs for several years then reopened. The 18 foot chamber has been in
>> and out of use for years. We had several smaller Hi-Vac ones (some 3' and
>> 5') used for laser communication testing, also 10 and 15 chambers used for
>> high altitude and low temp testing. 
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