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Real name: Mohamed Sami Gattoufi


Post by samigattoufi » Fri Jul 13, 2018 10:01 am

Hi, so i'd like to know if i can use plexiglass in my vacuum chamber. I mean is it safe for the fusion?

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Richard Hull
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Post by Richard Hull » Fri Jul 13, 2018 6:56 pm

Glass and any form of plastic vessel will not support fusion work.

Richard Hull
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Joshua Guertler
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Post by Joshua Guertler » Sat Jul 14, 2018 1:55 pm

Greetings Mohamed,

It seems that Mr. Hull has already summarized the issue at such a low pressure range and that most glass-based devices would implode at the 5-20 micron range. If I am not too late, I would recommend using two 1/8" thick stainless steel hemispheres put together to form a sphere. Typically, first time fusor-builders will use hemispheres with a diameter of 6 to 8 inches to have easy control over the deuterium and vacuum pressure.

The FAQs should provide you with all of these details and more on chamber construction.

Good luck!

Joshua Guertler

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Rich Feldman
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Post by Rich Feldman » Sat Jul 14, 2018 11:49 pm

>> most glass-based devices would implode at the 5-20 micron range.

Joshua, we have to interrupt before a serious misconception is propagated.
How much does the implosion risk change between a 7.6 torr vacuum and a 7.6 micron vacuum?
The material stresses, from exterior-interior pressure difference, increase from 99% of maximum to 99.999% of maximum.

A glass or plastic vessel could be safe or unsafe against risk of implosion, depending on its physical design. (Consider light bulbs and fluorescent lamps.) But the difference between any old vacuum, not counting vacuum cleaners, and "high vacuum" is minor.
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Post by ian_krase » Sun Jul 15, 2018 12:16 am

Glass is risky in vacuum because its brittle, but in general vacuum forces are not overwhelming to a chamber that is either properly stiffened or just thick-walled. 1/8th inch is thicker than needed for the typical vacuum hemisphere chamber, 1/16th inch (1.5 mm) is enough.

However, Plexiglass will leak plastic vapor into the vacuum, and then it won't be a vacuum anymore. It will get much worse if you have plasma.

Also, even demo fusor operation typically produces enough heat, over time, to melt plastic. Then it will definitely implode.

Use metal (mostly) and glass (for windows or low-end demo fusors).

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Post by Jerry Biehler » Sun Jul 15, 2018 8:50 am

No, glass is fine for a lot of vacuum systems. They have been used for over 100 years and are still used. Plexi is an OK vacuum material as well there are commercial turbo pumped systems available with acrylic doors or bell jars. I have an 18x18" glass bell jar and it is very nice. I have had it down to the -8 range.

But they are not good for fusors because fusors generate electron and ion beams inside the chamber which will spot heat the chamber which will be real bad for both glass and plastic bell jars. You could build a metal enclosure inside the bell jar but by the time you do that you could just build a metal vacuum chamber like everyone else does.

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