Fusor Forums

Slow and steady I will replace my leaky and problematic glass bowl chamber to a new and better chamber.

I´m thinking of using 2 stainless steel salad bowls to build my "classical" hemisphere shaped chamber (as I´ve read in the forum that others have used the same)

But wouldn´t the tiny thickness of the steel (0.5mm) cause outgassing problems when under high vacuum from a diffusion pump? I´m worried because my primary pump is very weak (2CFM).

How is the thickness relevant? Outgassing is the release of an adsorbed layer of gases from the surface. However, the thin metal may distort when pumped down, causing leaks.
Tony Webb

Frederick -

It will tend to outgas more rapidly. Other than being more flexible than the thicker walled standard SS hemispheres, the salad bowls could work well.

You'll need a skilled MIG/TIG welder to join the bowl halves to mounting flanges. The thinner wall material is easier to burn through.

Dave Cooper


.

If the material is thin you could try brazing it with a silver brazing alloy, unless it gets hot, the Cd found in easy to find common silver brazing alloy will not be a problem. There are however special silver brazing alloys for vacuum use, where the Cd is replaced with Sn, if this is an issue.

The added bonus would be no welder required, just a torch. Handy and Harmon carries the complete alloy line, they also offer great technical advice. I used such a Silver, Copper, Tin vacuum rated brazing alloy to put a new flange on a DP, with excellent results, no regrets.

Fredrik,

It has been done before...

Go for the smaller size Ikea bowls.

Steven

Fredrik

As one who has sucessfully used glass bowls, I would point out they need to be prepared first to obtain a good seal. Grind the rims with diamond paste to get them flat for a seal.

viewtopic.php?f=18&t=7715#p55674

photo 5

P.S. Dont forget the plastic sheilds when working under vacuum. A layer of wax at the joint will ensure a complete seal capable of 10E-8 - and no outgas problems [ well minor ones ] A piece of rubber from a car tube to make a band will give a rough seal when compressed with a SS compression ring and some vac grease on the joint surface.

Thank for the link John, and for setting a new thought train in motion for me, real cool, it reminded me of grinding telescope mirrors a long time ago. During this time one "first timer" ground and polished his 8" F-6 pyrex mirror to 1/10 wave, yes it was part luck, but he was just to dam happy to be reminded of this.

I mention this because the same abrasive techniques used for telescope mirror grinding, will work great here, and these sites represent an easy path to all of the materials required etc. I just never thought that they would be that useful with fusors and high vacuum.

This may be the key to fabricating an insulating spacer for the ion source which I am building, since they do not seem to sell insulating spacers compatable with standard ISO/NW vacuum fittings. If I am wrong on this, and there is a source, then please let me know however.

PS: At least you do not have to do a pitch lap : )

Thanks for all your responses.

I believe that I have the small bowl with its diameter of 4.72" from ikea. From your responses it seems like outgassing wouldn´t be much of a problem.

I will try to make this chamber as cheap as possible. My plans for the chamber constuction is the following: 2 mounting flanges to connect the two steel bowls, one small boron glass viewport and then I will buy one fitting for my vacuum pump system to the chamber. To save some money I will drill a hole directly into the bowl and weld a large sparkplug as a HV feed through. As for the deuterium gas inlet I will almost do the same, just drill a hole and weld a small pipe to it.

For the welding I will probably ask some guys at a steel workshop to do it as they have all the tools needed for construction. Before I buy anything I will ask the physics department in my local university if they have anything that I might need

is it anything I´m missing or will this be enough? I know that the cost of all the vacuum components will be quite high but approximately how much do you guys think this would cost me?

The expensive/difficult to obtain parts are the flanges and a flexi-pipe to connect the diff pump to the foreline pump.

Everything else can be obtained cheap on Ebay.

(This was our experience, anyway.)