Glass vacuum chambers, a good idea, or just plain stupid?

[ZackaryMiller]

I am, as stated in my introduction post, developing a concept for a small fusor to serve as a neutron source as well as for demonstration purposes (and the possibility of building other fusion devices in the future). To that end I have been looking at the parts list that I will need and have found that the most expensive part is the vacuum chamber. Unfortunately I do not have the money for the machining equipment needed to make one, so purchasing one is the only option.

So far I have been looking for high vacuum chambers and have found that the costs of such things tend to be in the 1,000 USD range, far too expensive for a demonstration of nuclear fusion and a weak neutron source. To solve the problem with cost I have been looking at the possibility of using a glass vacuum chamber rather than a metal one. The potental advantages to such a chamber are as listed as follows

-low cost (200-300 USD for one of comparable size to a 1000 USD one)
-if I do demonstrate it in the school gymnasium or theater before my fellow students (or even in front of a single class) they could see the fusion reaction (though they may need high density goggles)
-glass is transparent to x rays and other radiation, thus allowing me to design unique set ups to use said radiation, however this poses a hazard and will need separate shielding when used at home.

Due to the above I am leaning towards using a glass vacuum chamber, however I want a second opinion before I use it for my demo fusor as I want to re-use the vacuum chamber for a most decidedly less demo fusor.

[Richard Hull]

It is generally held that you will not be able to do good usable, even moderately sustained, amateur fusion in a fusor within any glass enclosure. Give that idea up now before you get in trouble trying to do it. Discussed many times here. It is very stupid and always will be.

Richard Hull

[ZackaryMiller]

Thank you for the quick response, but may I ask why that is so?

[John Futter]

Zackary
Ok you have a star mode in your glass chamber lets say eight radials from the star @ 40kV 20mA
now that's 800 watts of input
each radial might have 70 -130 watts of power in an electron beam coming from the central grid

I can tell you now a radial of this power striking the glass and locally heating it will result tremendous stress in the glass

you guessed it!, it will crack -implode--vacuum escapes--but probably you don't from high speed glass shards

also very few experiments need an isotropic x-ray /neutron source

much better to contain and let it out via a viewport in a known direction

[Bob Reite]

The neutrons will be attenuated very little by a stainless steel chamber.

[Doug Browning]

Occasionally large diffusion pumps come up for sale on Ebay that are cheap enough to just use one for a vacuum tank. Right now there is an 11" OD flanged one listed at $99. There were a bunch of VHS-10 units that sold this last summer for $350. They were almost the size of a barrel.

[Jeroen Vriesman]

This is how a "big glass bell jar" is constructed, it's an old 4kW plasma cleaner.

The jar is big, about 40cm diameter and about 60cm high, the ring on top of the jar is pushed downwards by 2 pneumatic linear actuators, and the jar is inside a metal cage.

A scratch on the jar can break the glass when it's under vacuum (just like the scratch from a normal glass cutter).

For the kind of power you need for a fusor a steel vacuum chamber is much easier.