Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Few fusor questions...
Date: Mar 27, 4:01 pm
Poster: Richard Hull

On Mar 27, 4:01 pm, Richard Hull wrote:

>I'm using plumbing for the system (which will be running on normal air) which is not made of stainless steel, so I'm worried about it outgassing. What I'm currently using is cast iron plumbing, but I might have to live with brass. The zinc inside of the brass is what worries me most though. If anyone could possibly tell me if and how much these two metals outgas, or possibly even a list of metals that outgas if its not too much trouble, I would be very grateful. Thanks.


Welcome to the fold! Glad to have another active person chime in.

As for a list of materials suitable for vacuum, glass, stainless steel, and copper are the better materials. It is those unseen or un-thought of items that kill you like solder, epoxy, fluxes, greases, waxes, etc that can kill you pumps efficiency through outgassing.

Both cast iron and brass are terrible outgassers. Cast iron is the absolute worst of the two. Countless trillions of pits and micro holes. The stuff is as pourous as a sponge! The zinc in Brass, while a source of outgassing, can be used in the micron range if continuously pumped while running. Just don't expect to valve off, stop the pump, and come back in an hour with a usable vacuum still in there. Small brass fitting s are of little harm in the micron range, but making a brass bell jar or vessel with a huge surface area is.

I know that a demo fusor is not a critical thing and I used some terrible materials on my first demo fusor back in 1997, but any serious effort at fusion demands the best components you can muster.

One needs to have as few variables creeping into the more complicated task of fusion as possible. Sloppy or outgassing components in a system would just boost the hassle factor up through the roof.

The cast iron has got to go. A solid copper plumbing system is just fine. Steve Hansen published his amateur vacuum station construction details in the "Bell Jar" periodical a few years back and he hits a nice vacuum using just copper. You can soft solder the thing together, but hard silver soldering with non-cadmium silver solder is the prefered method. Hopefully, the plumbing is very short. On my fusor the run from pump to fusor, including trap, is 12 inches. I consider that terrible! I have a friend who pumps a 6"X12" bell jar down using 1/4 tubing curled up on his bench!! (maybe 24"). He starts the pump, takes th' kids to school, feeds th' fish, goes to the grocery and when he gets back he is at 100 microns. In molecular flow regime, the molecules richocett up one end of that tube and down the other only rarely exiting into the pump head.

Good luck with your effort. Lose the cast iron and keep those lines large in diameter and very short.

Richard Hull